source: vbox/trunk/src/VBox/VMM/VMMR0/GMMR0.cpp@ 7692

/* $Id: GMMR0.cpp 6636 2008-01-30 21:46:07Z vboxsync $ */
/** @file
 * GMM - Global Memory Manager.
 */

/*
 * Copyright (C) 2007 innotek GmbH
 *
 * This file is part of VirtualBox Open Source Edition (OSE), as
 * available from http://www.virtualbox.org. This file is free software;
 * you can redistribute it and/or modify it under the terms of the GNU
 * General Public License (GPL) as published by the Free Software
 * Foundation, in version 2 as it comes in the "COPYING" file of the
 * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
 */


/** @page pg_gmm    GMM - The Global Memory Manager
 *
 * As the name indicates, this component is responsible for global memory
 * management. Currently only guest RAM is allocated from the GMM, but this
 * may change to include shadow page tables and other bits later.
 *
 * Guest RAM is managed as individual pages, but allocated from the host OS
 * in chunks for reasons of portability / efficiency. To minimize the memory
 * footprint all tracking structure must be as small as possible without
 * unnecessary performance penalties.
 *
 * The allocation chunks has fixed sized, the size defined at compile time
 * by the #GMM_CHUNK_SIZE \#define.
 *
 * Each chunk is given an unquie ID. Each page also has a unique ID. The
 * relation ship between the two IDs is:
 * @code
 *  GMM_CHUNK_SHIFT = log2(GMM_CHUNK_SIZE / PAGE_SIZE);
 *  idPage = (idChunk << GMM_CHUNK_SHIFT) | iPage;
 * @endcode
 * Where iPage is the index of the page within the chunk. This ID scheme
 * permits for efficient chunk and page lookup, but it relies on the chunk size
 * to be set at compile time. The chunks are organized in an AVL tree with their
 * IDs being the keys.
 *
 * The physical address of each page in an allocation chunk is maintained by
 * the #RTR0MEMOBJ and obtained using #RTR0MemObjGetPagePhysAddr. There is no
 * need to duplicate this information (it'll cost 8-bytes per page if we did).
 *
 * So what do we need to track per page? Most importantly we need to know
 * which state the page is in:
 *   - Private - Allocated for (eventually) backing one particular VM page.
 *   - Shared  - Readonly page that is used by one or more VMs and treated
 *               as COW by PGM.
 *   - Free    - Not used by anyone.
 *
 * For the page replacement operations (sharing, defragmenting and freeing)
 * to be somewhat efficient, private pages needs to be associated with a
 * particular page in a particular VM.
 *
 * Tracking the usage of shared pages is impractical and expensive, so we'll
 * settle for a reference counting system instead.
 *
 * Free pages will be chained on LIFOs
 *
 * On 64-bit systems we will use a 64-bit bitfield per page, while on 32-bit
 * systems a 32-bit bitfield will have to suffice because of address space
 * limitations. The #GMMPAGE structure shows the details.
 *
 *
 * @section sec_gmm_alloc_strat Page Allocation Strategy
 *
 * The strategy for allocating pages has to take fragmentation and shared
 * pages into account, or we may end up with with 2000 chunks with only
 * a few pages in each. Shared pages cannot easily be reallocated because
 * of the inaccurate usage accounting (see above). Private pages can be
 * reallocated by a defragmentation thread in the same manner that sharing
 * is done.
 *
 * The first approach is to manage the free pages in two sets depending on
 * whether they are mainly for the allocation of shared or private pages.
 * In the initial implementation there will be almost no possibility for
 * mixing shared and private pages in the same chunk (only if we're really
 * stressed on memory), but when we implement forking of VMs and have to
 * deal with lots of COW pages it'll start getting kind of interesting.
 *
 * The sets are lists of chunks with approximately the same number of
 * free pages. Say the chunk size is 1MB, meaning 256 pages, and a set
 * consists of 16 lists. So, the first list will contain the chunks with
 * 1-7 free pages, the second covers 8-15, and so on. The chunks will be
 * moved between the lists as pages are freed up or allocated.
 *
 *
 * @section sec_gmm_costs       Costs
 *
 * The per page cost in kernel space is 32-bit plus whatever RTR0MEMOBJ
 * entails. In addition there is the chunk cost of approximately
 * (sizeof(RT0MEMOBJ) + sizof(CHUNK)) / 2^CHUNK_SHIFT bytes per page.
 *
 * On Windows the per page #RTR0MEMOBJ cost is 32-bit on 32-bit windows
 * and 64-bit on 64-bit windows (a PFN_NUMBER in the MDL). So, 64-bit per page.
 * The cost on Linux is identical, but here it's because of sizeof(struct page *).
 *
 *
 * @section sec_gmm_legacy      Legacy Mode for Non-Tier-1 Platforms
 *
 * In legacy mode the page source is locked user pages and not
 * #RTR0MemObjAllocPhysNC, this means that a page can only be allocated
 * by the VM that locked it. We will make no attempt at implementing
 * page sharing on these systems, just do enough to make it all work.
 *
 *
 * @subsection sub_gmm_locking  Serializing
 *
 * One simple fast mutex will be employed in the initial implementation, not
 * two as metioned in @ref subsec_pgmPhys_Serializing.
 *
 * @see @ref subsec_pgmPhys_Serializing
 *
 *
 * @section sec_gmm_overcommit  Memory Over-Commitment Management
 *
 * The GVM will have to do the system wide memory over-commitment
 * management. My current ideas are:
 *      - Per VM oc policy that indicates how much to initially commit
 *        to it and what to do in a out-of-memory situation.
 *      - Prevent overtaxing the host.
 *
 * There are some challenges here, the main ones are configurability and
 * security. Should we for instance permit anyone to request 100% memory
 * commitment? Who should be allowed to do runtime adjustments of the
 * config. And how to prevent these settings from being lost when the last
 * VM process exits? The solution is probably to have an optional root
 * daemon the will keep VMMR0.r0 in memory and enable the security measures.
 *
 *
 *
 * @section sec_gmm_numa  NUMA
 *
 * NUMA considerations will be designed and implemented a bit later.
 *
 * The preliminary guesses is that we will have to try allocate memory as
 * close as possible to the CPUs the VM is executed on (EMT and additional CPU
 * threads). Which means it's mostly about allocation and sharing policies.
 * Both the scheduler and allocator interface will to supply some NUMA info
 * and we'll need to have a way to calc access costs.
 *
 */


/*******************************************************************************
*   Header Files                                                               *
*******************************************************************************/
#define LOG_GROUP LOG_GROUP_GMM
#include <VBox/gmm.h>
#include "GMMR0Internal.h"
#include <VBox/gvm.h>
#include <VBox/log.h>
#include <VBox/param.h>
#include <VBox/err.h>
#include <iprt/avl.h>
#include <iprt/mem.h>
#include <iprt/memobj.h>
#include <iprt/semaphore.h>
#include <iprt/string.h>


/*******************************************************************************
*   Structures and Typedefs                                                    *
*******************************************************************************/
/** Pointer to set of free chunks.  */
typedef struct GMMCHUNKFREESET *PGMMCHUNKFREESET;

/** Pointer to a GMM allocation chunk. */
typedef struct GMMCHUNK *PGMMCHUNK;

/**
 * The per-page tracking structure employed by the GMM.
 *
 * On 32-bit hosts we'll some trickery is necessary to compress all
 * the information into 32-bits. When the fSharedFree member is set,
 * the 30th bit decides whether it's a free page or not.
 *
 * Because of the different layout on 32-bit and 64-bit hosts, macros
 * are used to get and set some of the data.
 */
typedef union GMMPAGE
{
#if HC_ARCH_BITS == 64
    /** Unsigned integer view. */
    uint64_t u;

    /** The common view. */
    struct GMMPAGECOMMON
    {
        uint32_t uStuff1 : 32;
        uint32_t uStuff2 : 20;
        /** The page state. */
        uint32_t    u2State : 2;
    } Common;

    /** The view of a private page. */
    struct GMMPAGEPRIVATE
    {
        /** The guest page frame number. (Max addressable: 2 ^ 44 - 16) */
        uint32_t    pfn;
        /** The GVM handle. (64K VMs) */
        uint32_t    hGVM : 16;
        /** Reserved. */
        uint32_t    u16Reserved : 14;
        /** The page state. */
        uint32_t    u2State : 2;
    } Private;

    /** The view of a shared page. */
    struct GMMPAGESHARED
    {
        /** The reference count. */
        uint32_t    cRefs;
        /** Reserved. Checksum or something? Two hGVMs for forking? */
        uint32_t    u30Reserved : 30;
        /** The page state. */
        uint32_t    u2State : 2;
    } Shared;

    /** The view of a free page. */
    struct GMMPAGEFREE
    {
        /** The index of the next page in the free list. UINT16_MAX is NIL. */
        uint16_t    iNext;
        /** Reserved. Checksum or something? */
        uint16_t    u16Reserved0;
        /** Reserved. Checksum or something? */
        uint32_t    u30Reserved1 : 30;
        /** The page state. */
        uint32_t    u2State : 2;
    } Free;

#else /* 32-bit */
    /** Unsigned integer view. */
    uint32_t u;

    /** The common view. */
    struct GMMPAGECOMMON
    {
        uint32_t    uStuff : 30;
        /** The page state. */
        uint32_t    u2State : 2;
    } Common;

    /** The view of a private page. */
    struct GMMPAGEPRIVATE
    {
        /** The guest page frame number. (Max addressable: 2 ^ 36) */
        uint32_t    pfn : 24;
        /** The GVM handle. (127 VMs) */
        uint32_t    hGVM : 7;
        /** The top page state bit, MBZ. */
        uint32_t    fZero : 1;
    } Private;

    /** The view of a shared page. */
    struct GMMPAGESHARED
    {
        /** The reference count. */
        uint32_t    cRefs : 30;
        /** The page state. */
        uint32_t    u2State : 2;
    } Shared;

    /** The view of a free page. */
    struct GMMPAGEFREE
    {
        /** The index of the next page in the free list. UINT16_MAX is NIL. */
        uint32_t    iNext : 16;
        /** Reserved. Checksum or something? */
        uint32_t    u14Reserved : 14;
        /** The page state. */
        uint32_t    u2State : 2;
    } Free;
#endif
} GMMPAGE;
AssertCompileSize(GMMPAGE, sizeof(RTHCUINTPTR));
/** Pointer to a GMMPAGE. */
typedef GMMPAGE *PGMMPAGE;


/** @name The Page States.
 * @{ */
/** A private page. */
#define GMM_PAGE_STATE_PRIVATE          0
/** A private page - alternative value used on the 32-bit implemenation.
 * This will never be used on 64-bit hosts. */
#define GMM_PAGE_STATE_PRIVATE_32       1
/** A shared page. */
#define GMM_PAGE_STATE_SHARED           2
/** A free page. */
#define GMM_PAGE_STATE_FREE             3
/** @} */


/** @def GMM_PAGE_IS_PRIVATE
 *
 * @returns true if free, false if not.
 * @param   pPage       The GMM page.
 */
#if HC_ARCH_BITS == 64
# define GMM_PAGE_IS_PRIVATE(pPage) ( (pPage)->Common.u2State == GMM_PAGE_STATE_PRIVATE )
#else
# define GMM_PAGE_IS_PRIVATE(pPage) ( (pPage)->Private.fZero == 0 )
#endif

/** @def GMM_PAGE_IS_FREE
 *
 * @returns true if free, false if not.
 * @param   pPage       The GMM page.
 */
#define GMM_PAGE_IS_SHARED(pPage)   ( (pPage)->Common.u2State == GMM_PAGE_STATE_SHARED )

/** @def GMM_PAGE_IS_FREE
 *
 * @returns true if free, false if not.
 * @param   pPage       The GMM page.
 */
#define GMM_PAGE_IS_FREE(pPage)     ( (pPage)->Common.u2State == GMM_PAGE_STATE_FREE )

/** @def GMM_PAGE_PFN_END
 * The end of the the valid guest pfn range, {0..GMM_PAGE_PFN_END-1}.
 * @remark Some of the values outside the range has special meaning, see related \#defines.
 */
#if HC_ARCH_BITS == 64
# define GMM_PAGE_PFN_END           UINT32_C(0xfffffff0)
#else
# define GMM_PAGE_PFN_END           UINT32_C(0x00fffff0)
#endif

/** @def GMM_PAGE_PFN_UNSHAREABLE
 * Indicates that this page isn't used for normal guest memory and thus isn't shareable.
 */
#if HC_ARCH_BITS == 64
# define GMM_PAGE_PFN_UNSHAREABLE   UINT32_C(0xfffffff1)
#else
# define GMM_PAGE_PFN_UNSHAREABLE   UINT32_C(0x00fffff1)
#endif

/** @def GMM_GCPHYS_END
 * The end of the valid guest physical address as it applies to GMM pages.
 *
 * This must reflect the constraints imposed by the RTGCPHYS type and
 * the guest page frame number used internally in GMMPAGE. */
#define GMM_GCPHYS_END              UINT32_C(0xfffff000)


/**
 * A GMM allocation chunk ring-3 mapping record.
 *
 * This should really be associated with a session and not a VM, but
 * it's simpler to associated with a VM and cleanup with the VM object
 * is destroyed.
 */
typedef struct GMMCHUNKMAP
{
    /** The mapping object. */
    RTR0MEMOBJ      MapObj;
    /** The VM owning the mapping. */
    PGVM            pGVM;
} GMMCHUNKMAP;
/** Pointer to a GMM allocation chunk mapping. */
typedef struct GMMCHUNKMAP *PGMMCHUNKMAP;


/**
 * A GMM allocation chunk.
 */
typedef struct GMMCHUNK
{
    /** The AVL node core.
     * The Key is the chunk ID. */
    AVLU32NODECORE      Core;
    /** The memory object.
     * Either from RTR0MemObjAllocPhysNC or RTR0MemObjLockUser depending on
     * what the host can dish up with. */
    RTR0MEMOBJ          MemObj;
    /** Pointer to the next chunk in the free list. */
    PGMMCHUNK           pFreeNext;
    /** Pointer to the previous chunk in the free list. */
    PGMMCHUNK           pFreePrev;
    /** Pointer to the free set this chunk belongs to. NULL for
     * chunks with no free pages. */
    PGMMCHUNKFREESET    pSet;
    /** Pointer to an array of mappings. */
    PGMMCHUNKMAP        paMappings;
    /** The number of mappings. */
    uint16_t            cMappings;
    /** The head of the list of free pages. UINT16_MAX is the NIL value. */
    uint16_t            iFreeHead;
    /** The number of free pages. */
    uint16_t            cFree;
    /** The GVM handle of the VM that first allocated pages from this chunk, this
     * is used as a preference when there are several chunks to choose from.
     * When in legacy mode this isn't a preference any longer. */
    uint16_t            hGVM;
    /** The number of private pages. */
    uint16_t            cPrivate;
    /** The number of shared pages. */
    uint16_t            cShared;
#if HC_ARCH_BITS == 64
    /** Reserved for later. */
    uint16_t            au16Reserved[2];
#endif
    /** The pages. */
    GMMPAGE             aPages[GMM_CHUNK_SIZE >> PAGE_SHIFT];
} GMMCHUNK;


/**
 * An allocation chunk TLB entry.
 */
typedef struct GMMCHUNKTLBE
{
    /** The chunk id. */
    uint32_t        idChunk;
    /** Pointer to the chunk. */
    PGMMCHUNK       pChunk;
} GMMCHUNKTLBE;
/** Pointer to an allocation chunk TLB entry. */
typedef GMMCHUNKTLBE *PGMMCHUNKTLBE;


/** The number of entries tin the allocation chunk TLB. */
#define GMM_CHUNKTLB_ENTRIES        32
/** Gets the TLB entry index for the given Chunk ID. */
#define GMM_CHUNKTLB_IDX(idChunk)   ( (idChunk) & (GMM_CHUNKTLB_ENTRIES - 1) )

/**
 * An allocation chunk TLB.
 */
typedef struct GMMCHUNKTLB
{
    /** The TLB entries. */
    GMMCHUNKTLBE    aEntries[GMM_CHUNKTLB_ENTRIES];
} GMMCHUNKTLB;
/** Pointer to an allocation chunk TLB. */
typedef GMMCHUNKTLB *PGMMCHUNKTLB;


/** The number of lists in set. */
#define GMM_CHUNK_FREE_SET_LISTS    16
/** The GMMCHUNK::cFree shift count. */
#define GMM_CHUNK_FREE_SET_SHIFT    4
/** The GMMCHUNK::cFree mask for use when considering relinking a chunk. */
#define GMM_CHUNK_FREE_SET_MASK     15

/**
 * A set of free chunks.
 */
typedef struct GMMCHUNKFREESET
{
    /** The number of free pages in the set. */
    uint64_t        cPages;
    /**  */
    PGMMCHUNK       apLists[GMM_CHUNK_FREE_SET_LISTS];
} GMMCHUNKFREESET;


/**
 * The GMM instance data.
 */
typedef struct GMM
{
    /** Magic / eye catcher. GMM_MAGIC */
    uint32_t            u32Magic;
    /** The fast mutex protecting the GMM.
     * More fine grained locking can be implemented later if necessary. */
    RTSEMFASTMUTEX      Mtx;
    /** The chunk tree. */
    PAVLU32NODECORE     pChunks;
    /** The chunk TLB. */
    GMMCHUNKTLB         ChunkTLB;
    /** The private free set. */
    GMMCHUNKFREESET     Private;
    /** The shared free set. */
    GMMCHUNKFREESET     Shared;

    /** The maximum number of pages we're allowed to allocate.
     * @gcfgm   64-bit GMM/MaxPages Direct.
     * @gcfgm   32-bit GMM/PctPages Relative to the number of host pages. */
    uint64_t            cMaxPages;
    /** The number of pages that has been reserved.
     * The deal is that cReservedPages - cOverCommittedPages <= cMaxPages. */
    uint64_t            cReservedPages;
    /** The number of pages that we have over-committed in reservations. */
    uint64_t            cOverCommittedPages;
    /** The number of actually allocated (committed if you like) pages. */
    uint64_t            cAllocatedPages;
    /** The number of pages that are shared. A subset of cAllocatedPages. */
    uint64_t            cSharedPages;
    /** The number of pages that are shared that has been left behind by
     * VMs not doing proper cleanups. */
    uint64_t            cLeftBehindSharedPages;
    /** The number of allocation chunks.
     * (The number of pages we've allocated from the host can be derived from this.) */
    uint32_t            cChunks;
    /** The number of current ballooned pages. */
    uint64_t            cBalloonedPages;

    /** The legacy mode indicator.
     * This is determined at initialization time. */
    bool                fLegacyMode;
    /** The number of registered VMs. */
    uint16_t            cRegisteredVMs;

    /** The previous allocated Chunk ID.
     * Used as a hint to avoid scanning the whole bitmap. */
    uint32_t            idChunkPrev;
    /** Chunk ID allocation bitmap.
     * Bits of allocated IDs are set, free ones are cleared.
     * The NIL id (0) is marked allocated. */
    uint32_t            bmChunkId[(GMM_CHUNKID_LAST + 32) >> 10];
} GMM;
/** Pointer to the GMM instance. */
typedef GMM *PGMM;

/** The value of GMM::u32Magic (Katsuhiro Otomo). */
#define GMM_MAGIC       0x19540414


/*******************************************************************************
*   Global Variables                                                           *
*******************************************************************************/
/** Pointer to the GMM instance data. */
static PGMM g_pGMM = NULL;

/** Macro for obtaining and validating the g_pGMM pointer.
 * On failure it will return from the invoking function with the specified return value.
 *
 * @param   pGMM    The name of the pGMM variable.
 * @param   rc      The return value on failure. Use VERR_INTERNAL_ERROR for
 *                  VBox status codes.
 */
#define GMM_GET_VALID_INSTANCE(pGMM, rc) \
    do { \
        (pGMM) = g_pGMM; \
        AssertPtrReturn((pGMM), (rc)); \
        AssertMsgReturn((pGMM)->u32Magic == GMM_MAGIC, ("%p - %#x\n", (pGMM), (pGMM)->u32Magic), (rc)); \
    } while (0)

/** Macro for obtaining and validating the g_pGMM pointer, void function variant.
 * On failure it will return from the invoking function.
 *
 * @param   pGMM    The name of the pGMM variable.
 */
#define GMM_GET_VALID_INSTANCE_VOID(pGMM) \
    do { \
        (pGMM) = g_pGMM; \
        AssertPtrReturnVoid((pGMM)); \
        AssertMsgReturnVoid((pGMM)->u32Magic == GMM_MAGIC, ("%p - %#x\n", (pGMM), (pGMM)->u32Magic)); \
    } while (0)


/*******************************************************************************
*   Internal Functions                                                         *
*******************************************************************************/
static DECLCALLBACK(int) gmmR0TermDestroyChunk(PAVLU32NODECORE pNode, void *pvGMM);
static DECLCALLBACK(int) gmmR0CleanupVMScanChunk(PAVLU32NODECORE pNode, void *pvGMM);
/*static*/ DECLCALLBACK(int) gmmR0CleanupVMDestroyChunk(PAVLU32NODECORE pNode, void *pvGVM);
DECLINLINE(void) gmmR0LinkChunk(PGMMCHUNK pChunk, PGMMCHUNKFREESET pSet);
DECLINLINE(void) gmmR0UnlinkChunk(PGMMCHUNK pChunk);
static void gmmR0FreeChunk(PGMM pGMM, PGMMCHUNK pChunk);
static void gmmR0FreeSharedPage(PGMM pGMM, uint32_t idPage, PGMMPAGE pPage);



/**
 * Initializes the GMM component.
 *
 * This is called when the VMMR0.r0 module is loaded and protected by the
 * loader semaphore.
 *
 * @returns VBox status code.
 */
GMMR0DECL(int) GMMR0Init(void)
{
    LogFlow(("GMMInit:\n"));

    /*
     * Allocate the instance data and the lock(s).
     */
    PGMM pGMM = (PGMM)RTMemAllocZ(sizeof(*pGMM));
    if (!pGMM)
        return VERR_NO_MEMORY;
    pGMM->u32Magic = GMM_MAGIC;
    for (unsigned i = 0; i < RT_ELEMENTS(pGMM->ChunkTLB.aEntries); i++)
        pGMM->ChunkTLB.aEntries[i].idChunk = NIL_GMM_CHUNKID;
    ASMBitSet(&pGMM->bmChunkId[0], NIL_GMM_CHUNKID);

    int rc = RTSemFastMutexCreate(&pGMM->Mtx);
    if (RT_SUCCESS(rc))
    {
        /*
         * Check and see if RTR0MemObjAllocPhysNC works.
         */
#if 0 /* later */
        RTR0MEMOBJ MemObj;
        rc = RTR0MemObjAllocPhysNC(&MemObj, _64K, NIL_RTHCPHYS);
        if (RT_SUCCESS(rc))
        {
            rc = RTR0MemObjFree(MemObj, true);
            AssertRC(rc);
        }
        else if (rc == VERR_NOT_SUPPORTED)
            pGMM->fLegacyMode = true;
        else
            SUPR0Printf("GMMR0Init: RTR0MemObjAllocPhysNC(,64K,Any) -> %d!\n", rc);
#else
        pGMM->fLegacyMode = true;
#endif

        g_pGMM = pGMM;
        LogFlow(("GMMInit: pGMM=%p fLegacy=%RTbool\n", pGMM, pGMM->fLegacyMode));
        return VINF_SUCCESS;
    }

    RTMemFree(pGMM);
    SUPR0Printf("GMMR0Init: failed! rc=%d\n", rc);
    return rc;
}


/**
 * Terminates the GMM component.
 */
GMMR0DECL(void) GMMR0Term(void)
{
    LogFlow(("GMMTerm:\n"));

    /*
     * Take care / be paranoid...
     */
    PGMM pGMM = g_pGMM;
    if (!VALID_PTR(pGMM))
        return;
    if (pGMM->u32Magic != GMM_MAGIC)
    {
        SUPR0Printf("GMMR0Term: u32Magic=%#x\n", pGMM->u32Magic);
        return;
    }

    /*
     * Undo what init did and free all the resources we've acquired.
     */
    /* Destroy the fundamentals. */
    g_pGMM = NULL;
    pGMM->u32Magic++;
    RTSemFastMutexDestroy(pGMM->Mtx);
    pGMM->Mtx = NIL_RTSEMFASTMUTEX;

    /* free any chunks still hanging around. */
    RTAvlU32Destroy(&pGMM->pChunks, gmmR0TermDestroyChunk, pGMM);

    /* finally the instance data itself. */
    RTMemFree(pGMM);
    LogFlow(("GMMTerm: done\n"));
}


/**
 * RTAvlU32Destroy callback.
 *
 * @returns 0
 * @param   pNode   The node to destroy.
 * @param   pvGMM   The GMM handle.
 */
static DECLCALLBACK(int) gmmR0TermDestroyChunk(PAVLU32NODECORE pNode, void *pvGMM)
{
    PGMMCHUNK pChunk = (PGMMCHUNK)pNode;

    if (pChunk->cFree != (GMM_CHUNK_SIZE >> PAGE_SHIFT))
        SUPR0Printf("GMMR0Term: %p/%#x: cFree=%d cPrivate=%d cShared=%d cMappings=%d\n", pChunk,
                    pChunk->Core.Key, pChunk->cFree, pChunk->cPrivate, pChunk->cShared, pChunk->cMappings);

    int rc = RTR0MemObjFree(pChunk->MemObj, true /* fFreeMappings */);
    if (RT_FAILURE(rc))
    {
        SUPR0Printf("GMMR0Term: %p/%#x: RTRMemObjFree(%p,true) -> %d (cMappings=%d)\n", pChunk,
                    pChunk->Core.Key, pChunk->MemObj, rc, pChunk->cMappings);
        AssertRC(rc);
    }
    pChunk->MemObj = NIL_RTR0MEMOBJ;

    RTMemFree(pChunk->paMappings);
    pChunk->paMappings = NULL;

    RTMemFree(pChunk);
    NOREF(pvGMM);
    return 0;
}


/**
 * Initializes the per-VM data for the GMM.
 *
 * This is called from within the GVMM lock (from GVMMR0CreateVM)
 * and should only initialize the data members so GMMR0CleanupVM
 * can deal with them. We reserve no memory or anything here,
 * that's done later in GMMR0InitVM.
 *
 * @param   pGVM    Pointer to the Global VM structure.
 */
GMMR0DECL(void) GMMR0InitPerVMData(PGVM pGVM)
{
    AssertCompile(RT_SIZEOFMEMB(GVM,gmm.s) <= RT_SIZEOFMEMB(GVM,gmm.padding));
    AssertRelease(RT_SIZEOFMEMB(GVM,gmm.s) <= RT_SIZEOFMEMB(GVM,gmm.padding));

    pGVM->gmm.s.enmPolicy = GMMOCPOLICY_INVALID;
    pGVM->gmm.s.enmPriority = GMMPRIORITY_INVALID;
    pGVM->gmm.s.fMayAllocate = false;
}


/**
 * Cleans up when a VM is terminating.
 *
 * @param   pGVM    Pointer to the Global VM structure.
 */
GMMR0DECL(void) GMMR0CleanupVM(PGVM pGVM)
{
    LogFlow(("GMMR0CleanupVM: pGVM=%p:{.pVM=%p, .hSelf=%#x}\n", pGVM, pGVM->pVM, pGVM->hSelf));

    PGMM pGMM;
    GMM_GET_VALID_INSTANCE_VOID(pGMM);

    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);

    /*
     * The policy is 'INVALID' until the initial reservation
     * request has been serviced.
     */
    if (    pGVM->gmm.s.enmPolicy > GMMOCPOLICY_INVALID
        ||  pGVM->gmm.s.enmPolicy < GMMOCPOLICY_END)
    {
        /*
         * If it's the last VM around, we can skip walking all the chunk looking
         * for the pages owned by this VM and instead flush the whole shebang.
         *
         * This takes care of the eventuality that a VM has left shared page
         * references behind (shouldn't happen of course, but you never know).
         */
        Assert(pGMM->cRegisteredVMs);
        pGMM->cRegisteredVMs--;
#if 0 /* disabled so it won't hide bugs. */
        if (!pGMM->cRegisteredVMs)
        {
            RTAvlU32Destroy(&pGMM->pChunks, gmmR0CleanupVMDestroyChunk, pGMM);

            for (unsigned i = 0; i < RT_ELEMENTS(pGMM->ChunkTLB.aEntries); i++)
            {
                pGMM->ChunkTLB.aEntries[i].idChunk = NIL_GMM_CHUNKID;
                pGMM->ChunkTLB.aEntries[i].pChunk = NULL;
            }

            memset(&pGMM->Private, 0, sizeof(pGMM->Private));
            memset(&pGMM->Shared, 0, sizeof(pGMM->Shared));

            memset(&pGMM->bmChunkId[0], 0, sizeof(pGMM->bmChunkId));
            ASMBitSet(&pGMM->bmChunkId[0], NIL_GMM_CHUNKID);

            pGMM->cReservedPages = 0;
            pGMM->cOverCommittedPages = 0;
            pGMM->cAllocatedPages = 0;
            pGMM->cSharedPages = 0;
            pGMM->cLeftBehindSharedPages = 0;
            pGMM->cChunks = 0;
            pGMM->cBalloonedPages = 0;
        }
        else
#endif
        {
            /*
             * Walk the entire pool looking for pages that belongs to this VM
             * and left over mappings. (This'll only catch private pages, shared
             * pages will be 'left behind'.)
             */
            uint64_t cPrivatePages = pGVM->gmm.s.cPrivatePages; /* save */
            RTAvlU32DoWithAll(&pGMM->pChunks, true /* fFromLeft */, gmmR0CleanupVMScanChunk, pGVM);
            if (pGVM->gmm.s.cPrivatePages)
                SUPR0Printf("GMMR0CleanupVM: hGVM=%#x has %#x private pages that cannot be found!\n", pGVM->hSelf, pGVM->gmm.s.cPrivatePages);
            pGMM->cAllocatedPages -= cPrivatePages;

            /* free empty chunks. */
            if (cPrivatePages)
            {
                PGMMCHUNK pCur = pGMM->Private.apLists[RT_ELEMENTS(pGMM->Private.apLists) - 1];
                while (pCur)
                {
                    PGMMCHUNK pNext = pCur->pFreeNext;
                    if (    pCur->cFree == GMM_CHUNK_NUM_PAGES
                        &&  (!pGMM->fLegacyMode || pCur->hGVM == pGVM->hSelf))
                        gmmR0FreeChunk(pGMM, pCur);
                    pCur = pNext;
                }
            }

            /* account for shared pages that weren't freed. */
            if (pGVM->gmm.s.cSharedPages)
            {
                Assert(pGMM->cSharedPages >= pGVM->gmm.s.cSharedPages);
                SUPR0Printf("GMMR0CleanupVM: hGVM=%#x left %#x shared pages behind!\n", pGVM->hSelf, pGVM->gmm.s.cSharedPages);
                pGMM->cLeftBehindSharedPages += pGVM->gmm.s.cSharedPages;
            }

            /*
             * Update the over-commitment management statistics.
             */
            pGMM->cReservedPages -= pGVM->gmm.s.Reserved.cBasePages
                                  + pGVM->gmm.s.Reserved.cFixedPages
                                  + pGVM->gmm.s.Reserved.cShadowPages;
            switch (pGVM->gmm.s.enmPolicy)
            {
                case GMMOCPOLICY_NO_OC:
                    break;
                default:
                    /** @todo Update GMM->cOverCommittedPages */
                    break;
            }
        }
    }

    /* zap the GVM data. */
    pGVM->gmm.s.enmPolicy = GMMOCPOLICY_INVALID;
    pGVM->gmm.s.enmPriority = GMMPRIORITY_INVALID;
    pGVM->gmm.s.fMayAllocate = false;

    RTSemFastMutexRelease(pGMM->Mtx);

    LogFlow(("GMMR0CleanupVM: returns\n"));
}


/**
 * RTAvlU32DoWithAll callback.
 *
 * @returns 0
 * @param   pNode   The node to search.
 * @param   pvGVM   Pointer to the shared VM structure.
 */
static DECLCALLBACK(int) gmmR0CleanupVMScanChunk(PAVLU32NODECORE pNode, void *pvGVM)
{
    PGMMCHUNK pChunk = (PGMMCHUNK)pNode;
    PGVM pGVM = (PGVM)pvGVM;

    /*
     * Look for pages belonging to the VM.
     * (Perform some internal checks while we're scanning.)
     */
#ifndef VBOX_STRICT
    if (pChunk->cFree != (GMM_CHUNK_SIZE >> PAGE_SHIFT))
#endif
    {
        unsigned cPrivate = 0;
        unsigned cShared = 0;
        unsigned cFree = 0;

        uint16_t hGVM = pGVM->hSelf;
        unsigned iPage = (GMM_CHUNK_SIZE >> PAGE_SHIFT);
        while (iPage-- > 0)
            if (GMM_PAGE_IS_PRIVATE(&pChunk->aPages[iPage]))
            {
                if (pChunk->aPages[iPage].Private.hGVM == hGVM)
                {
                    /*
                     * Free the page.
                     *
                     * The reason for not using gmmR0FreePrivatePage here is that we
                     * must *not* cause the chunk to be freed from under us - we're in
                     * a AVL tree walk here.
                     */
                    pChunk->aPages[iPage].u = 0;
                    pChunk->aPages[iPage].Free.iNext = pChunk->iFreeHead;
                    pChunk->aPages[iPage].Free.u2State = GMM_PAGE_STATE_FREE;
                    pChunk->iFreeHead = iPage;
                    pChunk->cPrivate--;
                    if ((pChunk->cFree & GMM_CHUNK_FREE_SET_MASK) == 0)
                    {
                        gmmR0UnlinkChunk(pChunk);
                        pChunk->cFree++;
                        gmmR0LinkChunk(pChunk, pChunk->cShared ? &g_pGMM->Shared : &g_pGMM->Private);
                    }
                    else
                        pChunk->cFree++;
                    pGVM->gmm.s.cPrivatePages--;
                    cFree++;
                }
                else
                    cPrivate++;
            }
            else if (GMM_PAGE_IS_FREE(&pChunk->aPages[iPage]))
                cFree++;
            else
                cShared++;

        /*
         * Did it add up?
         */
        if (RT_UNLIKELY(    pChunk->cFree != cFree
                        ||  pChunk->cPrivate != cPrivate
                        ||  pChunk->cShared != cShared))
        {
            SUPR0Printf("gmmR0CleanupVMScanChunk: Chunk %p/%#x has bogus stats - free=%d/%d private=%d/%d shared=%d/%d\n",
                        pChunk->cFree, cFree, pChunk->cPrivate, cPrivate, pChunk->cShared, cShared);
            pChunk->cFree = cFree;
            pChunk->cPrivate = cPrivate;
            pChunk->cShared = cShared;
        }
    }

    /*
     * Look for the mapping belonging to the terminating VM.
     */
    for (unsigned i = 0; i < pChunk->cMappings; i++)
        if (pChunk->paMappings[i].pGVM == pGVM)
        {
            RTR0MEMOBJ MemObj = pChunk->paMappings[i].MapObj;

            pChunk->cMappings--;
            if (i < pChunk->cMappings)
                 pChunk->paMappings[i] = pChunk->paMappings[pChunk->cMappings];
            pChunk->paMappings[pChunk->cMappings].pGVM = NULL;
            pChunk->paMappings[pChunk->cMappings].MapObj = NIL_RTR0MEMOBJ;

            int rc = RTR0MemObjFree(MemObj, false /* fFreeMappings (NA) */);
            if (RT_FAILURE(rc))
            {
                SUPR0Printf("gmmR0CleanupVMScanChunk: %p/%#x: mapping #%x: RTRMemObjFree(%p,false) -> %d \n",
                            pChunk, pChunk->Core.Key, i, MemObj, rc);
                AssertRC(rc);
            }
            break;
        }

    /*
     * If not in legacy mode, we should reset the hGVM field
     * if it has our handle in it.
     */
    if (pChunk->hGVM == pGVM->hSelf)
    {
        if (!g_pGMM->fLegacyMode)
            pChunk->hGVM = NIL_GVM_HANDLE;
        else if (pChunk->cFree != GMM_CHUNK_NUM_PAGES)
        {
            SUPR0Printf("gmmR0CleanupVMScanChunk: %p/%#x: cFree=%#x - it should be 0 in legacy mode!\n",
                        pChunk, pChunk->Core.Key, pChunk->cFree);
            AssertMsgFailed(("%p/%#x: cFree=%#x - it should be 0 in legacy mode!\n", pChunk, pChunk->Core.Key, pChunk->cFree));

            gmmR0UnlinkChunk(pChunk);
            pChunk->cFree = GMM_CHUNK_NUM_PAGES;
            gmmR0LinkChunk(pChunk, pChunk->cShared ? &g_pGMM->Shared : &g_pGMM->Private);
        }
    }

    return 0;
}


/**
 * RTAvlU32Destroy callback for GMMR0CleanupVM.
 *
 * @returns 0
 * @param   pNode   The node (allocation chunk) to destroy.
 * @param   pvGVM   Pointer to the shared VM structure.
 */
/*static*/ DECLCALLBACK(int) gmmR0CleanupVMDestroyChunk(PAVLU32NODECORE pNode, void *pvGVM)
{
    PGMMCHUNK pChunk = (PGMMCHUNK)pNode;
    PGVM pGVM = (PGVM)pvGVM;

    for (unsigned i = 0; i < pChunk->cMappings; i++)
    {
        if (pChunk->paMappings[i].pGVM != pGVM)
            SUPR0Printf("gmmR0CleanupVMDestroyChunk: %p/%#x: mapping #%x: pGVM=%p exepcted %p\n", pChunk,
                        pChunk->Core.Key, i, pChunk->paMappings[i].pGVM, pGVM);
        int rc = RTR0MemObjFree(pChunk->paMappings[i].MapObj, false /* fFreeMappings (NA) */);
        if (RT_FAILURE(rc))
        {
            SUPR0Printf("gmmR0CleanupVMDestroyChunk: %p/%#x: mapping #%x: RTRMemObjFree(%p,false) -> %d \n", pChunk,
                        pChunk->Core.Key, i, pChunk->paMappings[i].MapObj, rc);
            AssertRC(rc);
        }
    }

    int rc = RTR0MemObjFree(pChunk->MemObj, true /* fFreeMappings */);
    if (RT_FAILURE(rc))
    {
        SUPR0Printf("gmmR0CleanupVMDestroyChunk: %p/%#x: RTRMemObjFree(%p,true) -> %d (cMappings=%d)\n", pChunk,
                    pChunk->Core.Key, pChunk->MemObj, rc, pChunk->cMappings);
        AssertRC(rc);
    }
    pChunk->MemObj = NIL_RTR0MEMOBJ;

    RTMemFree(pChunk->paMappings);
    pChunk->paMappings = NULL;

    RTMemFree(pChunk);
    return 0;
}


/**
 * The initial resource reservations.
 *
 * This will make memory reservations according to policy and priority. If there isn't
 * sufficient resources available to sustain the VM this function will fail and all
 * future allocations requests will fail as well.
 *
 * These are just the initial reservations made very very early during the VM creation
 * process and will be adjusted later in the GMMR0UpdateReservation call after the
 * ring-3 init has completed.
 *
 * @returns VBox status code.
 * @retval  VERR_GMM_MEMORY_RESERVATION_DECLINED
 * @retval  VERR_GMM_
 *
 * @param   pVM             Pointer to the shared VM structure.
 * @param   cBasePages      The number of pages that may be allocated for the base RAM and ROMs.
 *                          This does not include MMIO2 and similar.
 * @param   cShadowPages    The number of pages that may be allocated for shadow pageing structures.
 * @param   cFixedPages     The number of pages that may be allocated for fixed objects like the
 *                          hyper heap, MMIO2 and similar.
 * @param   enmPolicy       The OC policy to use on this VM.
 * @param   enmPriority     The priority in an out-of-memory situation.
 *
 * @thread  The creator thread / EMT.
 */
GMMR0DECL(int) GMMR0InitialReservation(PVM pVM, uint64_t cBasePages, uint32_t cShadowPages, uint32_t cFixedPages,
                                       GMMOCPOLICY enmPolicy, GMMPRIORITY enmPriority)
{
    LogFlow(("GMMR0InitialReservation: pVM=%p cBasePages=%#llx cShadowPages=%#x cFixedPages=%#x enmPolicy=%d enmPriority=%d\n",
             pVM, cBasePages, cShadowPages, cFixedPages, enmPolicy, enmPriority));

    /*
     * Validate, get basics and take the semaphore.
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (!pGVM)
        return VERR_INVALID_PARAMETER;
    if (pGVM->hEMT != RTThreadNativeSelf())
        return VERR_NOT_OWNER;

    AssertReturn(cBasePages, VERR_INVALID_PARAMETER);
    AssertReturn(cShadowPages, VERR_INVALID_PARAMETER);
    AssertReturn(cFixedPages, VERR_INVALID_PARAMETER);
    AssertReturn(enmPolicy > GMMOCPOLICY_INVALID && enmPolicy < GMMOCPOLICY_END, VERR_INVALID_PARAMETER);
    AssertReturn(enmPriority > GMMPRIORITY_INVALID && enmPriority < GMMPRIORITY_END, VERR_INVALID_PARAMETER);

    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);

    if (    !pGVM->gmm.s.Reserved.cBasePages
        &&  !pGVM->gmm.s.Reserved.cFixedPages
        &&  !pGVM->gmm.s.Reserved.cShadowPages)
    {
        /*
         * Check if we can accomodate this.
         */
        /* ... later ... */
        if (RT_SUCCESS(rc))
        {
            /*
             * Update the records.
             */
            pGVM->gmm.s.Reserved.cBasePages = cBasePages;
            pGVM->gmm.s.Reserved.cFixedPages = cFixedPages;
            pGVM->gmm.s.Reserved.cShadowPages = cShadowPages;
            pGVM->gmm.s.enmPolicy = enmPolicy;
            pGVM->gmm.s.enmPriority = enmPriority;
            pGVM->gmm.s.fMayAllocate = true;

            pGMM->cReservedPages += cBasePages + cFixedPages + cShadowPages;
            pGMM->cRegisteredVMs++;
        }
    }
    else
        rc = VERR_WRONG_ORDER;

    RTSemFastMutexRelease(pGMM->Mtx);
    LogFlow(("GMMR0InitialReservation: returns %Rrc\n", rc));
    return rc;
}


/**
 * VMMR0 request wrapper for GMMR0InitialReservation.
 *
 * @returns see GMMR0InitialReservation.
 * @param   pVM             Pointer to the shared VM structure.
 * @param   pReq            The request packet.
 */
GMMR0DECL(int) GMMR0InitialReservationReq(PVM pVM, PGMMINITIALRESERVATIONREQ pReq)
{
    /*
     * Validate input and pass it on.
     */
    AssertPtrReturn(pVM, VERR_INVALID_POINTER);
    AssertPtrReturn(pReq, VERR_INVALID_POINTER);
    AssertMsgReturn(pReq->Hdr.cbReq == sizeof(*pReq), ("%#x != %#x\n", pReq->Hdr.cbReq, sizeof(*pReq)), VERR_INVALID_PARAMETER);

    return GMMR0InitialReservation(pVM, pReq->cBasePages, pReq->cShadowPages, pReq->cFixedPages, pReq->enmPolicy, pReq->enmPriority);
}


/**
 * This updates the memory reservation with the additional MMIO2 and ROM pages.
 *
 * @returns VBox status code.
 * @retval  VERR_GMM_MEMORY_RESERVATION_DECLINED
 *
 * @param   pVM             Pointer to the shared VM structure.
 * @param   cBasePages      The number of pages that may be allocated for the base RAM and ROMs.
 *                          This does not include MMIO2 and similar.
 * @param   cShadowPages    The number of pages that may be allocated for shadow pageing structures.
 * @param   cFixedPages     The number of pages that may be allocated for fixed objects like the
 *                          hyper heap, MMIO2 and similar.
 *
 * @thread  EMT.
 */
GMMR0DECL(int) GMMR0UpdateReservation(PVM pVM, uint64_t cBasePages, uint32_t cShadowPages, uint32_t cFixedPages)
{
    LogFlow(("GMMR0UpdateReservation: pVM=%p cBasePages=%#llx cShadowPages=%#x cFixedPages=%#x\n",
             pVM, cBasePages, cShadowPages, cFixedPages));

    /*
     * Validate, get basics and take the semaphore.
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (!pGVM)
        return VERR_INVALID_PARAMETER;
    if (pGVM->hEMT != RTThreadNativeSelf())
        return VERR_NOT_OWNER;

    AssertReturn(cBasePages, VERR_INVALID_PARAMETER);
    AssertReturn(cShadowPages, VERR_INVALID_PARAMETER);
    AssertReturn(cFixedPages, VERR_INVALID_PARAMETER);

    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);

    if (    pGVM->gmm.s.Reserved.cBasePages
        &&  pGVM->gmm.s.Reserved.cFixedPages
        &&  pGVM->gmm.s.Reserved.cShadowPages)
    {
        /*
         * Check if we can accomodate this.
         */
        /* ... later ... */
        if (RT_SUCCESS(rc))
        {
            /*
             * Update the records.
             */
            pGMM->cReservedPages -= pGVM->gmm.s.Reserved.cBasePages
                                  + pGVM->gmm.s.Reserved.cFixedPages
                                  + pGVM->gmm.s.Reserved.cShadowPages;
            pGMM->cReservedPages += cBasePages + cFixedPages + cShadowPages;

            pGVM->gmm.s.Reserved.cBasePages = cBasePages;
            pGVM->gmm.s.Reserved.cFixedPages = cFixedPages;
            pGVM->gmm.s.Reserved.cShadowPages = cShadowPages;
        }
    }
    else
        rc = VERR_WRONG_ORDER;

    RTSemFastMutexRelease(pGMM->Mtx);
    LogFlow(("GMMR0UpdateReservation: returns %Rrc\n", rc));
    return rc;
}


/**
 * VMMR0 request wrapper for GMMR0UpdateReservation.
 *
 * @returns see GMMR0UpdateReservation.
 * @param   pVM             Pointer to the shared VM structure.
 * @param   pReq            The request packet.
 */
GMMR0DECL(int) GMMR0UpdateReservationReq(PVM pVM, PGMMUPDATERESERVATIONREQ pReq)
{
    /*
     * Validate input and pass it on.
     */
    AssertPtrReturn(pVM, VERR_INVALID_POINTER);
    AssertPtrReturn(pReq, VERR_INVALID_POINTER);
    AssertMsgReturn(pReq->Hdr.cbReq == sizeof(*pReq), ("%#x != %#x\n", pReq->Hdr.cbReq, sizeof(*pReq)), VERR_INVALID_PARAMETER);

    return GMMR0UpdateReservation(pVM, pReq->cBasePages, pReq->cShadowPages, pReq->cFixedPages);
}


/**
 * Looks up a chunk in the tree and fill in the TLB entry for it.
 *
 * This is not expected to fail and will bitch if it does.
 *
 * @returns Pointer to the allocation chunk, NULL if not found.
 * @param   pGMM        Pointer to the GMM instance.
 * @param   idChunk     The ID of the chunk to find.
 * @param   pTlbe       Pointer to the TLB entry.
 */
static PGMMCHUNK gmmR0GetChunkSlow(PGMM pGMM, uint32_t idChunk, PGMMCHUNKTLBE pTlbe)
{
    PGMMCHUNK pChunk = (PGMMCHUNK)RTAvlU32Get(&pGMM->pChunks, idChunk);
    AssertMsgReturn(pChunk, ("Chunk %#x not found!\n", idChunk), NULL);
    pTlbe->idChunk = idChunk;
    pTlbe->pChunk = pChunk;
    return pChunk;
}


/**
 * Finds a allocation chunk.
 *
 * This is not expected to fail and will bitch if it does.
 *
 * @returns Pointer to the allocation chunk, NULL if not found.
 * @param   pGMM        Pointer to the GMM instance.
 * @param   idChunk     The ID of the chunk to find.
 */
DECLINLINE(PGMMCHUNK) gmmR0GetChunk(PGMM pGMM, uint32_t idChunk)
{
    /*
     * Do a TLB lookup, branch if not in the TLB.
     */
    PGMMCHUNKTLBE pTlbe = &pGMM->ChunkTLB.aEntries[GMM_CHUNKTLB_IDX(idChunk)];
    if (    pTlbe->idChunk != idChunk
        ||  !pTlbe->pChunk)
        return gmmR0GetChunkSlow(pGMM, idChunk, pTlbe);
    return pTlbe->pChunk;
}


/**
 * Finds a page.
 *
 * This is not expected to fail and will bitch if it does.
 *
 * @returns Pointer to the page, NULL if not found.
 * @param   pGMM        Pointer to the GMM instance.
 * @param   idPage      The ID of the page to find.
 */
DECLINLINE(PGMMPAGE) gmmR0GetPage(PGMM pGMM, uint32_t idPage)
{
    PGMMCHUNK pChunk = gmmR0GetChunk(pGMM, idPage >> GMM_CHUNKID_SHIFT);
    if (RT_LIKELY(pChunk))
        return &pChunk->aPages[idPage & GMM_PAGEID_IDX_MASK];
    return NULL;
}


/**
 * Unlinks the chunk from the free list it's currently on (if any).
 *
 * @param   pChunk      The allocation chunk.
 */
DECLINLINE(void) gmmR0UnlinkChunk(PGMMCHUNK pChunk)
{
    PGMMCHUNKFREESET pSet = pChunk->pSet;
    if (RT_LIKELY(pSet))
    {
        pSet->cPages -= pChunk->cFree;

        PGMMCHUNK pPrev = pChunk->pFreePrev;
        PGMMCHUNK pNext = pChunk->pFreeNext;
        if (pPrev)
            pPrev->pFreeNext = pNext;
        else
            pSet->apLists[(pChunk->cFree - 1) >> GMM_CHUNK_FREE_SET_SHIFT] = pNext;
        if (pNext)
            pNext->pFreePrev = pPrev;

        pChunk->pSet = NULL;
        pChunk->pFreeNext = NULL;
        pChunk->pFreePrev = NULL;
    }
    else
    {
        Assert(!pChunk->pFreeNext);
        Assert(!pChunk->pFreePrev);
        Assert(!pChunk->cFree);
    }
}


/**
 * Links the chunk onto the appropriate free list in the specified free set.
 *
 * If no free entries, it's not linked into any list.
 *
 * @param   pChunk      The allocation chunk.
 * @param   pSet        The free set.
 */
DECLINLINE(void) gmmR0LinkChunk(PGMMCHUNK pChunk, PGMMCHUNKFREESET pSet)
{
    Assert(!pChunk->pSet);
    Assert(!pChunk->pFreeNext);
    Assert(!pChunk->pFreePrev);

    if (pChunk->cFree > 0)
    {
        pChunk->pFreePrev = NULL;
        unsigned iList = (pChunk->cFree - 1) >> GMM_CHUNK_FREE_SET_SHIFT;
        pChunk->pFreeNext = pSet->apLists[iList];
        pSet->apLists[iList] = pChunk;

        pSet->cPages += pChunk->cFree;
    }
}


/**
 * Frees a Chunk ID.
 *
 * @param   pGMM        Pointer to the GMM instance.
 * @param   idChunk     The Chunk ID to free.
 */
static void gmmR0FreeChunkId(PGMM pGMM, uint32_t idChunk)
{
    Assert(idChunk != NIL_GMM_CHUNKID);
    Assert(ASMBitTest(&pGMM->bmChunkId[0], idChunk));
    ASMAtomicBitClear(&pGMM->bmChunkId[0], idChunk);
}


/**
 * Allocates a new Chunk ID.
 *
 * @returns The Chunk ID.
 * @param   pGMM        Pointer to the GMM instance.
 */
static uint32_t gmmR0AllocateChunkId(PGMM pGMM)
{
    AssertCompile(!((GMM_CHUNKID_LAST + 1) & 31)); /* must be a multiple of 32 */
    AssertCompile(NIL_GMM_CHUNKID == 0);

    /*
     * Try the next sequential one.
     */
    int32_t idChunk = ++pGMM->idChunkPrev;
#if 0 /* test the fallback first */
    if (    idChunk <= GMM_CHUNKID_LAST
        &&  idChunk > NIL_GMM_CHUNKID
        &&  !ASMAtomicBitTestAndSet(&pVMM->bmChunkId[0], idChunk))
        return idChunk;
#endif

    /*
     * Scan sequentially from the last one.
     */
    if (    (uint32_t)idChunk < GMM_CHUNKID_LAST
        &&  idChunk > NIL_GMM_CHUNKID)
    {
        idChunk = ASMBitNextClear(&pGMM->bmChunkId[0], GMM_CHUNKID_LAST + 1, idChunk);
        if (idChunk > NIL_GMM_CHUNKID)
            return pGMM->idChunkPrev = idChunk;
    }

    /*
     * Ok, scan from the start.
     * We're not racing anyone, so there is no need to expect failures or have restart loops.
     */
    idChunk = ASMBitFirstClear(&pGMM->bmChunkId[0], GMM_CHUNKID_LAST + 1);
    AssertMsgReturn(idChunk > NIL_GMM_CHUNKID, ("%d\n", idChunk), NIL_GVM_HANDLE);
    AssertMsgReturn(!ASMAtomicBitTestAndSet(&pGMM->bmChunkId[0], idChunk), ("%d\n", idChunk), NIL_GVM_HANDLE);

    return pGMM->idChunkPrev = idChunk;
}


/**
 * Registers a new chunk of memory.
 *
 * This is called by both gmmR0AllocateOneChunk and GMMR0SeedChunk.
 *
 * @returns VBox status code.
 * @param   pGMM        Pointer to the GMM instance.
 * @param   pSet        Pointer to the set.
 * @param   MemObj      The memory object for the chunk.
 * @param   hGVM        The hGVM value. (Only used by GMMR0SeedChunk.)
 */
static int gmmR0RegisterChunk(PGMM pGMM, PGMMCHUNKFREESET pSet, RTR0MEMOBJ MemObj, uint16_t hGVM)
{
    int rc;
    PGMMCHUNK pChunk = (PGMMCHUNK)RTMemAllocZ(sizeof(*pChunk));
    if (pChunk)
    {
        /*
         * Initialize it.
         */
        pChunk->MemObj = MemObj;
        pChunk->cFree = GMM_CHUNK_NUM_PAGES;
        pChunk->hGVM = hGVM;
        pChunk->iFreeHead = 0;
        for (unsigned iPage = 0; iPage < RT_ELEMENTS(pChunk->aPages) - 1; iPage++)
        {
            pChunk->aPages[iPage].Free.u2State = GMM_PAGE_STATE_FREE;
            pChunk->aPages[iPage].Free.iNext = iPage + 1;
        }
        pChunk->aPages[RT_ELEMENTS(pChunk->aPages) - 1].Free.u2State = GMM_PAGE_STATE_FREE;
        pChunk->aPages[RT_ELEMENTS(pChunk->aPages) - 1].Free.iNext = UINT16_MAX;

        /*
         * Allocate a Chunk ID and insert it into the tree.
         * It doesn't cost anything to be careful here.
         */
        pChunk->Core.Key = gmmR0AllocateChunkId(pGMM);
        if (    pChunk->Core.Key != NIL_GMM_CHUNKID
            &&  pChunk->Core.Key <= GMM_CHUNKID_LAST
            &&  RTAvlU32Insert(&pGMM->pChunks, &pChunk->Core))
        {
            pGMM->cChunks++;
            gmmR0LinkChunk(pChunk, pSet);
            return VINF_SUCCESS;
        }

        rc = VERR_INTERNAL_ERROR;
        RTMemFree(pChunk);
    }
    else
        rc = VERR_NO_MEMORY;
    return rc;
}


/**
 * Allocate one new chunk and add it to the specified free set.
 *
 * @returns VBox status code.
 * @param   pGMM        Pointer to the GMM instance.
 * @param   pSet        Pointer to the set.
 */
static int gmmR0AllocateOneChunk(PGMM pGMM, PGMMCHUNKFREESET pSet)
{
    /*
     * Allocate the memory.
     */
    RTR0MEMOBJ MemObj;
    int rc = RTR0MemObjAllocPhysNC(&MemObj, GMM_CHUNK_SIZE, NIL_RTHCPHYS);
    if (RT_SUCCESS(rc))
    {
        rc = gmmR0RegisterChunk(pGMM, pSet, MemObj, NIL_GVM_HANDLE);
        if (RT_FAILURE(rc))
            RTR0MemObjFree(MemObj, false /* fFreeMappings */);
    }
    return rc;
}


/**
 * Attempts to allocate more pages until the requested amount is met.
 *
 * @returns VBox status code.
 * @param   pGMM        Pointer to the GMM instance data.
 * @param   pSet        Pointer to the free set to grow.
 * @param   cPages      The number of pages needed.
 */
static int gmmR0AllocateMoreChunks(PGMM pGMM, PGMMCHUNKFREESET pSet, uint32_t cPages)
{
    Assert(!pGMM->fLegacyMode);

    /*
     * Try steal free chunks from the other set first. (Only take 100% free chunks.)
     */
    PGMMCHUNKFREESET pOtherSet = pSet == &pGMM->Private ? &pGMM->Shared : &pGMM->Private;
    while (     pSet->cPages < cPages
           &&   pOtherSet->cPages >= GMM_CHUNK_NUM_PAGES)
    {
        PGMMCHUNK pChunk = pOtherSet->apLists[GMM_CHUNK_FREE_SET_LISTS - 1];
        while (pChunk && pChunk->cFree != GMM_CHUNK_NUM_PAGES)
            pChunk = pChunk->pFreeNext;
        if (!pChunk)
            break;

        gmmR0UnlinkChunk(pChunk);
        gmmR0LinkChunk(pChunk, pSet);
    }

    /*
     * If we need still more pages, allocate new chunks.
     */
    while (pSet->cPages < cPages)
    {
        int rc = gmmR0AllocateOneChunk(pGMM, pSet);
        if (RT_FAILURE(rc))
            return rc;
    }

    return VINF_SUCCESS;
}


/**
 * Allocates one page.
 *
 * Worker for gmmR0AllocatePages.
 *
 * @param   pGMM        Pointer to the GMM instance data.
 * @param   hGVM        The GVM handle of the VM requesting memory.
 * @param   pChunk      The chunk to allocate it from.
 * @param   pPageDesc   The page descriptor.
 */
static void gmmR0AllocatePage(PGMM pGMM, uint32_t hGVM, PGMMCHUNK pChunk, PGMMPAGEDESC pPageDesc)
{
    /* update the chunk stats. */
    if (pChunk->hGVM == NIL_GVM_HANDLE)
        pChunk->hGVM = hGVM;
    Assert(pChunk->cFree);
    pChunk->cFree--;

    /* unlink the first free page. */
    const uint32_t iPage = pChunk->iFreeHead;
    AssertReleaseMsg(iPage < RT_ELEMENTS(pChunk->aPages), ("%d\n", iPage));
    PGMMPAGE pPage = &pChunk->aPages[iPage];
    Assert(GMM_PAGE_IS_FREE(pPage));
    pChunk->iFreeHead = pPage->Free.iNext;

    /* make the page private. */
    pPage->u = 0;
    AssertCompile(GMM_PAGE_STATE_PRIVATE == 0);
    pPage->Private.hGVM = hGVM;
    AssertCompile(NIL_RTHCPHYS >= GMM_GCPHYS_END);
    AssertCompile(GMM_GCPHYS_UNSHAREABLE >= GMM_GCPHYS_END);
    if (pPageDesc->HCPhysGCPhys < GMM_GCPHYS_END)
        pPage->Private.pfn = pPageDesc->HCPhysGCPhys >> PAGE_SHIFT;
    else
        pPage->Private.pfn = GMM_PAGE_PFN_UNSHAREABLE; /* unshareable / unassigned - same thing. */

    /* update the page descriptor. */
    pPageDesc->HCPhysGCPhys = RTR0MemObjGetPagePhysAddr(pChunk->MemObj, iPage);
    Assert(pPageDesc->HCPhysGCPhys != NIL_RTHCPHYS);
    pPageDesc->idPage = (pChunk->Core.Key << GMM_CHUNKID_SHIFT) | iPage;
    pPageDesc->idSharedPage = NIL_GMM_PAGEID;
}


/**
 * Common worker for GMMR0AllocateHandyPages and GMMR0AllocatePages.
 *
 * @returns VBox status code:
 * @retval  xxx
 *
 * @param   pGMM                Pointer to the GMM instance data.
 * @param   pGVM                Pointer to the shared VM structure.
 * @param   cPages              The number of pages to allocate.
 * @param   paPages             Pointer to the page descriptors.
 *                              See GMMPAGEDESC for details on what is expected on input.
 * @param   enmAccount          The account to charge.
 */
static int gmmR0AllocatePages(PGMM pGMM, PGVM pGVM, uint32_t cPages, PGMMPAGEDESC paPages, GMMACCOUNT enmAccount)
{
    /*
     * Check allocation limits.
     */
    if (RT_UNLIKELY(pGMM->cAllocatedPages + cPages > pGMM->cMaxPages))
        return VERR_GMM_HIT_GLOBAL_LIMIT;

    switch (enmAccount)
    {
        case GMMACCOUNT_BASE:
            if (RT_UNLIKELY(pGVM->gmm.s.Allocated.cBasePages + cPages > pGVM->gmm.s.Reserved.cBasePages))
            {
                Log(("gmmR0AllocatePages: Reserved=%#llx Allocated+Requested=%#llx+%#x!\n",
                     pGVM->gmm.s.Reserved.cBasePages, pGVM->gmm.s.Allocated.cBasePages, cPages));
                return VERR_GMM_HIT_VM_ACCOUNT_LIMIT;
            }
            break;
        case GMMACCOUNT_SHADOW:
            if (RT_UNLIKELY(pGVM->gmm.s.Allocated.cShadowPages + cPages > pGVM->gmm.s.Reserved.cShadowPages))
            {
                Log(("gmmR0AllocatePages: Reserved=%#llx Allocated+Requested=%#llx+%#x!\n",
                     pGVM->gmm.s.Reserved.cShadowPages, pGVM->gmm.s.Allocated.cShadowPages, cPages));
                return VERR_GMM_HIT_VM_ACCOUNT_LIMIT;
            }
            break;
        case GMMACCOUNT_FIXED:
            if (RT_UNLIKELY(pGVM->gmm.s.Allocated.cFixedPages + cPages > pGVM->gmm.s.Reserved.cFixedPages))
            {
                Log(("gmmR0AllocatePages: Reserved=%#llx Allocated+Requested=%#llx+%#x!\n",
                     pGVM->gmm.s.Reserved.cFixedPages, pGVM->gmm.s.Allocated.cFixedPages, cPages));
                return VERR_GMM_HIT_VM_ACCOUNT_LIMIT;
            }
            break;
        default:
            AssertMsgFailedReturn(("enmAccount=%d\n", enmAccount), VERR_INTERNAL_ERROR);
    }

    /*
     * Check if we need to allocate more memory or not. In legacy mode this is
     * a bit extra work but it's easier to do it upfront than bailing out later.
     */
    PGMMCHUNKFREESET pSet = &pGMM->Private;
    if (pSet->cPages < cPages)
    {
        if (pGMM->fLegacyMode)
            return VERR_GMM_SEED_ME;

        int rc = gmmR0AllocateMoreChunks(pGMM, pSet, cPages);
        if (RT_FAILURE(rc))
            return rc;
        Assert(pSet->cPages >= cPages);
    }
    else if (pGMM->fLegacyMode)
    {
        uint16_t hGVM = pGVM->hSelf;
        uint32_t cPagesFound = 0;
        for (unsigned i = 0; i < RT_ELEMENTS(pSet->apLists); i++)
            for (PGMMCHUNK pCur = pSet->apLists[i]; pCur; pCur = pCur->pFreeNext)
                if (pCur->hGVM == hGVM)
                {
                    cPagesFound += pCur->cFree;
                    if (cPagesFound >= cPages)
                        break;
                }
        if (cPagesFound < cPages)
            return VERR_GMM_SEED_ME;
    }

    /*
     * Pick the pages.
     */
    uint16_t hGVM = pGVM->hSelf;
    uint32_t iPage = 0;
    for (unsigned i = 0; i < RT_ELEMENTS(pSet->apLists) && iPage < cPages; i++)
    {
        /* first round, pick from chunks with an affinity to the VM. */
        PGMMCHUNK pCur = pSet->apLists[i];
        while (pCur && iPage < cPages)
        {
            PGMMCHUNK pNext = pCur->pFreeNext;

            if (    pCur->hGVM == hGVM
                &&  (   pCur->cFree < GMM_CHUNK_NUM_PAGES
                     || pGMM->fLegacyMode))
            {
                gmmR0UnlinkChunk(pCur);
                for (; pCur->cFree && iPage < cPages; iPage++)
                    gmmR0AllocatePage(pGMM, hGVM, pCur, &paPages[iPage]);
                gmmR0LinkChunk(pCur, pSet);
            }

            pCur = pNext;
        }

        /* second round, take all free pages in this list. */
        if (!pGMM->fLegacyMode)
        {
            PGMMCHUNK pCur = pSet->apLists[i];
            while (pCur && iPage < cPages)
            {
                PGMMCHUNK pNext = pCur->pFreeNext;

                gmmR0UnlinkChunk(pCur);
                for (; pCur->cFree && iPage < cPages; iPage++)
                    gmmR0AllocatePage(pGMM, hGVM, pCur, &paPages[iPage]);
                gmmR0LinkChunk(pCur, pSet);

                pCur = pNext;
            }
        }
    }

    /*
     * Update the account.
     */
    switch (enmAccount)
    {
        case GMMACCOUNT_BASE:   pGVM->gmm.s.Allocated.cBasePages   += iPage;
        case GMMACCOUNT_SHADOW: pGVM->gmm.s.Allocated.cShadowPages += iPage;
        case GMMACCOUNT_FIXED:  pGVM->gmm.s.Allocated.cFixedPages  += iPage;
        default:
            AssertMsgFailedReturn(("enmAccount=%d\n", enmAccount), VERR_INTERNAL_ERROR);
    }
    pGVM->gmm.s.cPrivatePages += iPage;
    pGMM->cAllocatedPages     += iPage;

    AssertMsgReturn(iPage == cPages, ("%d != %d\n", iPage, cPages), VERR_INTERNAL_ERROR);

    /*
     * Check if we've reached some threshold and should kick one or two VMs and tell
     * them to inflate their balloons a bit more... later.
     */

    return VINF_SUCCESS;
}


/**
 * Updates the previous allocations and allocates more pages.
 *
 * The handy pages are always taken from the 'base' memory account.
 *
 * @returns VBox status code:
 * @retval  xxx
 *
 * @param   pVM                 Pointer to the shared VM structure.
 * @param   cPagesToUpdate      The number of pages to update (starting from the head).
 * @param   cPagesToAlloc       The number of pages to allocate (starting from the head).
 * @param   paPages             The array of page descriptors.
 *                              See GMMPAGEDESC for details on what is expected on input.
 * @thread  EMT.
 */
GMMR0DECL(int) GMMR0AllocateHandyPages(PVM pVM, uint32_t cPagesToUpdate, uint32_t cPagesToAlloc, PGMMPAGEDESC paPages)
{
    LogFlow(("GMMR0AllocateHandyPages: pVM=%p cPagesToUpdate=%#x cPagesToAlloc=%#x paPages=%p\n",
             pVM, cPagesToUpdate, cPagesToAlloc, paPages));

    /*
     * Validate, get basics and take the semaphore.
     * (This is a relatively busy path, so make predictions where possible.)
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (RT_UNLIKELY(!pGVM))
        return VERR_INVALID_PARAMETER;
    if (RT_UNLIKELY(pGVM->hEMT != RTThreadNativeSelf()))
        return VERR_NOT_OWNER;

    AssertPtrReturn(paPages, VERR_INVALID_PARAMETER);
    AssertMsgReturn(    (cPagesToUpdate && cPagesToUpdate < 1024)
                    ||  (cPagesToAlloc  && cPagesToAlloc < 1024),
                    ("cPagesToUpdate=%#x cPagesToAlloc=%#x\n", cPagesToUpdate, cPagesToAlloc),
                    VERR_INVALID_PARAMETER);

    unsigned iPage = 0;
    for (; iPage < cPagesToUpdate; iPage++)
    {
        AssertMsgReturn(    (    paPages[iPage].HCPhysGCPhys < GMM_GCPHYS_END
                             && !(paPages[iPage].HCPhysGCPhys & PAGE_OFFSET_MASK))
                        ||  paPages[iPage].HCPhysGCPhys == NIL_RTHCPHYS
                        ||  paPages[iPage].HCPhysGCPhys == GMM_GCPHYS_UNSHAREABLE,
                        ("#%#x: %RHp\n", iPage, paPages[iPage].HCPhysGCPhys),
                        VERR_INVALID_PARAMETER);
        AssertMsgReturn(    paPages[iPage].idPage <= GMM_PAGEID_LAST
                        /*||  paPages[iPage].idPage == NIL_GMM_PAGEID*/,
                        ("#%#x: %#x\n", iPage, paPages[iPage].idPage), VERR_INVALID_PARAMETER);
        AssertMsgReturn(    paPages[iPage].idPage <= GMM_PAGEID_LAST
                        /*||  paPages[iPage].idSharedPage == NIL_GMM_PAGEID*/,
                        ("#%#x: %#x\n", iPage, paPages[iPage].idSharedPage), VERR_INVALID_PARAMETER);
    }

    for (; iPage < cPagesToAlloc; iPage++)
    {
        AssertMsgReturn(paPages[iPage].HCPhysGCPhys == NIL_RTHCPHYS,   ("#%#x: %RHp\n", iPage, paPages[iPage].HCPhysGCPhys), VERR_INVALID_PARAMETER);
        AssertMsgReturn(paPages[iPage].idPage       == NIL_GMM_PAGEID, ("#%#x: %#x\n", iPage, paPages[iPage].idPage),        VERR_INVALID_PARAMETER);
        AssertMsgReturn(paPages[iPage].idSharedPage == NIL_GMM_PAGEID, ("#%#x: %#x\n", iPage, paPages[iPage].idSharedPage),  VERR_INVALID_PARAMETER);
    }

    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);

    /* No allocations before the initial reservation has been made! */
    if (RT_LIKELY(    pGVM->gmm.s.Reserved.cBasePages
                  &&  pGVM->gmm.s.Reserved.cFixedPages
                  &&  pGVM->gmm.s.Reserved.cShadowPages))
    {
        /*
         * Perform the updates.
         * Stop on the first error.
         */
        for (iPage = 0; iPage < cPagesToUpdate; iPage++)
        {
            if (paPages[iPage].idPage != NIL_GMM_PAGEID)
            {
                PGMMPAGE pPage = gmmR0GetPage(pGMM, paPages[iPage].idPage);
                if (RT_LIKELY(pPage))
                {
                    if (RT_LIKELY(GMM_PAGE_IS_PRIVATE(pPage)))
                    {
                        if (RT_LIKELY(pPage->Private.hGVM == pGVM->hSelf))
                        {
                            AssertCompile(NIL_RTHCPHYS > GMM_GCPHYS_END && GMM_GCPHYS_UNSHAREABLE > GMM_GCPHYS_END);
                            if (RT_LIKELY(paPages[iPage].HCPhysGCPhys < GMM_GCPHYS_END))
                                pPage->Private.pfn = paPages[iPage].HCPhysGCPhys >> PAGE_SHIFT;
                            else if (paPages[iPage].HCPhysGCPhys == GMM_GCPHYS_UNSHAREABLE)
                                pPage->Private.pfn = GMM_PAGE_PFN_UNSHAREABLE;
                            /* else: NIL_RTHCPHYS nothing */

                            paPages[iPage].idPage = NIL_GMM_PAGEID;
                            paPages[iPage].HCPhysGCPhys = NIL_RTHCPHYS;
                        }
                        else
                        {
                            Log(("GMMR0AllocateHandyPages: #%#x/%#x: Not owner! hGVM=%#x hSelf=%#x\n",
                                 iPage, paPages[iPage].idPage, pPage->Private.hGVM, pGVM->hSelf));
                            rc = VERR_GMM_NOT_PAGE_OWNER;
                            break;
                        }
                    }
                    else
                    {
                        Log(("GMMR0AllocateHandyPages: #%#x/%#x: Not private!\n", iPage, paPages[iPage].idPage));
                        rc = VERR_GMM_PAGE_NOT_PRIVATE;
                        break;
                    }
                }
                else
                {
                    Log(("GMMR0AllocateHandyPages: #%#x/%#x: Not found! (private)\n", iPage, paPages[iPage].idPage));
                    rc = VERR_GMM_PAGE_NOT_FOUND;
                    break;
                }
            }

            if (paPages[iPage].idSharedPage != NIL_GMM_PAGEID)
            {
                PGMMPAGE pPage = gmmR0GetPage(pGMM, paPages[iPage].idSharedPage);
                if (RT_LIKELY(pPage))
                {
                    if (RT_LIKELY(GMM_PAGE_IS_SHARED(pPage)))
                    {
                        AssertCompile(NIL_RTHCPHYS > GMM_GCPHYS_END && GMM_GCPHYS_UNSHAREABLE > GMM_GCPHYS_END);
                        Assert(pPage->Shared.cRefs);
                        Assert(pGVM->gmm.s.cSharedPages);
                        Assert(pGVM->gmm.s.Allocated.cBasePages);

                        pGVM->gmm.s.cSharedPages--;
                        pGVM->gmm.s.Allocated.cBasePages--;
                        if (!--pPage->Shared.cRefs)
                            gmmR0FreeSharedPage(pGMM, paPages[iPage].idSharedPage, pPage);

                        paPages[iPage].idSharedPage = NIL_GMM_PAGEID;
                    }
                    else
                    {
                        Log(("GMMR0AllocateHandyPages: #%#x/%#x: Not shared!\n", iPage, paPages[iPage].idSharedPage));
                        rc = VERR_GMM_PAGE_NOT_SHARED;
                        break;
                    }
                }
                else
                {
                    Log(("GMMR0AllocateHandyPages: #%#x/%#x: Not found! (shared)\n", iPage, paPages[iPage].idSharedPage));
                    rc = VERR_GMM_PAGE_NOT_FOUND;
                    break;
                }
            }
        }

        /*
         * Join paths with GMMR0AllocatePages for the allocation.
         */
        if (RT_SUCCESS(rc))
            rc = gmmR0AllocatePages(pGMM, pGVM, cPagesToAlloc, paPages, GMMACCOUNT_BASE);
    }
    else
        rc = VERR_WRONG_ORDER;

    RTSemFastMutexRelease(pGMM->Mtx);
    LogFlow(("GMMR0AllocateHandyPages: returns %Rrc\n", rc));
    return rc;
}


/**
 * Allocate one or more pages.
 *
 * This is typically used for ROMs and MMIO2 (VRAM) during VM creation.
 *
 * @returns VBox status code:
 * @retval  xxx
 *
 * @param   pVM                 Pointer to the shared VM structure.
 * @param   cPages              The number of pages to allocate.
 * @param   paPages             Pointer to the page descriptors.
 *                              See GMMPAGEDESC for details on what is expected on input.
 * @param   enmAccount          The account to charge.
 *
 * @thread  EMT.
 */
GMMR0DECL(int) GMMR0AllocatePages(PVM pVM, uint32_t cPages, PGMMPAGEDESC paPages, GMMACCOUNT enmAccount)
{
    LogFlow(("GMMR0AllocatePages: pVM=%p cPages=%#x paPages=%p enmAccount=%d\n", pVM, cPages, paPages, enmAccount));

    /*
     * Validate, get basics and take the semaphore.
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (!pGVM)
        return VERR_INVALID_PARAMETER;
    if (pGVM->hEMT != RTThreadNativeSelf())
        return VERR_NOT_OWNER;

    AssertPtrReturn(paPages, VERR_INVALID_PARAMETER);
    AssertMsgReturn(enmAccount > GMMACCOUNT_INVALID && enmAccount < GMMACCOUNT_END, ("%d\n", enmAccount), VERR_INVALID_PARAMETER);
    AssertMsgReturn(cPages > 0 && cPages < RT_BIT(32 - PAGE_SHIFT), ("%#x\n", cPages), VERR_INVALID_PARAMETER);

    for (unsigned iPage = 0; iPage < cPages; iPage++)
    {
        AssertMsgReturn(    paPages[iPage].HCPhysGCPhys == NIL_RTHCPHYS
                        ||  paPages[iPage].HCPhysGCPhys == GMM_GCPHYS_UNSHAREABLE
                        ||  (    enmAccount == GMMACCOUNT_BASE
                             &&  paPages[iPage].HCPhysGCPhys < GMM_GCPHYS_END
                             && !(paPages[iPage].HCPhysGCPhys & PAGE_OFFSET_MASK)),
                        ("#%#x: %RHp enmAccount=%d\n", iPage, paPages[iPage].HCPhysGCPhys, enmAccount),
                        VERR_INVALID_PARAMETER);
        AssertMsgReturn(paPages[iPage].idPage == NIL_GMM_PAGEID, ("#%#x: %#x\n", iPage, paPages[iPage].idPage), VERR_INVALID_PARAMETER);
        AssertMsgReturn(paPages[iPage].idSharedPage == NIL_GMM_PAGEID, ("#%#x: %#x\n", iPage, paPages[iPage].idSharedPage), VERR_INVALID_PARAMETER);
    }

    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);

    /* No allocations before the initial reservation has been made! */
    if (    pGVM->gmm.s.Reserved.cBasePages
        &&  pGVM->gmm.s.Reserved.cFixedPages
        &&  pGVM->gmm.s.Reserved.cShadowPages)
        rc = gmmR0AllocatePages(pGMM, pGVM, cPages, paPages, enmAccount);
    else
        rc = VERR_WRONG_ORDER;

    RTSemFastMutexRelease(pGMM->Mtx);
    LogFlow(("GMMR0UpdateReservation: returns %Rrc\n", rc));
    return rc;
}


/**
 * VMMR0 request wrapper for GMMR0AllocatePages.
 *
 * @returns see GMMR0AllocatePages.
 * @param   pVM             Pointer to the shared VM structure.
 * @param   pReq            The request packet.
 */
GMMR0DECL(int) GMMR0AllocatePagesReq(PVM pVM, PGMMALLOCATEPAGESREQ pReq)
{
    /*
     * Validate input and pass it on.
     */
    AssertPtrReturn(pVM, VERR_INVALID_POINTER);
    AssertPtrReturn(pReq, VERR_INVALID_POINTER);
    AssertMsgReturn(pReq->Hdr.cbReq >= RT_UOFFSETOF(GMMALLOCATEPAGESREQ, aPages[0]),
                    ("%#x < %#x\n", pReq->Hdr.cbReq, RT_UOFFSETOF(GMMALLOCATEPAGESREQ, aPages[0])),
                    VERR_INVALID_PARAMETER);
    AssertMsgReturn(pReq->Hdr.cbReq == RT_UOFFSETOF(GMMALLOCATEPAGESREQ, aPages[pReq->cPages]),
                    ("%#x != %#x\n", pReq->Hdr.cbReq, RT_UOFFSETOF(GMMALLOCATEPAGESREQ, aPages[pReq->cPages])),
                    VERR_INVALID_PARAMETER);

    return GMMR0AllocatePages(pVM, pReq->cPages, &pReq->aPages[0], pReq->enmAccount);
}


/**
 * Frees a chunk, giving it back to the host OS.
 *
 * @param   pGMM        Pointer to the GMM instance.
 * @param   pChunk      The chunk to free.
 */
static void gmmR0FreeChunk(PGMM pGMM, PGMMCHUNK pChunk)
{
    /*
     * If there are current mappings of the chunk, then request the
     * VMs to unmap them. Reposition the chunk in the free list so
     * it won't be a likely candidate for allocations.
     */
    if (pChunk->cMappings)
    {
        /** @todo R0 -> VM request */

    }
    else
    {
        /*
         * Try free the memory object.
         */
        int rc = RTR0MemObjFree(pChunk->MemObj, false /* fFreeMappings */);
        if (RT_SUCCESS(rc))
        {
            pChunk->MemObj = NIL_RTR0MEMOBJ;

            /*
             * Unlink it from everywhere.
             */
            gmmR0UnlinkChunk(pChunk);

            PAVLU32NODECORE pCore = RTAvlU32Remove(&pGMM->pChunks, pChunk->Core.Key);
            Assert(pCore == &pChunk->Core); NOREF(pCore);

            PGMMCHUNKTLBE pTlbe = &pGMM->ChunkTLB.aEntries[GMM_CHUNKTLB_IDX(pCore->Key)];
            if (pTlbe->pChunk == pChunk)
            {
                pTlbe->idChunk = NIL_GMM_CHUNKID;
                pTlbe->pChunk = NULL;
            }

            Assert(pGMM->cChunks > 0);
            pGMM->cChunks--;

            /*
             * Free the Chunk ID and struct.
             */
            gmmR0FreeChunkId(pGMM, pChunk->Core.Key);
            pChunk->Core.Key = NIL_GMM_CHUNKID;

            RTMemFree(pChunk->paMappings);
            pChunk->paMappings = NULL;

            RTMemFree(pChunk);
        }
        else
            AssertRC(rc);
    }
}


/**
 * Free page worker.
 *
 * The caller does all the statistic decrementing, we do all the incrementing.
 *
 * @param   pGMM        Pointer to the GMM instance data.
 * @param   pChunk      Pointer to the chunk this page belongs to.
 * @param   pPage       Pointer to the page.
 */
static void gmmR0FreePageWorker(PGMM pGMM, PGMMCHUNK pChunk, PGMMPAGE pPage)
{
    /*
     * Put the page on the free list.
     */
    pPage->u = 0;
    pPage->Free.u2State = GMM_PAGE_STATE_FREE;
    Assert(pChunk->iFreeHead < RT_ELEMENTS(pChunk->aPages) || pChunk->iFreeHead == UINT16_MAX);
    pPage->Free.iNext = pChunk->iFreeHead;
    pChunk->iFreeHead = pPage - &pChunk->aPages[0];

    /*
     * Update statistics (the cShared/cPrivate stats are up to date already),
     * and relink the chunk if necessary.
     */
    if ((pChunk->cFree & GMM_CHUNK_FREE_SET_MASK) == 0)
    {
        gmmR0UnlinkChunk(pChunk);
        pChunk->cFree++;
        gmmR0LinkChunk(pChunk, pChunk->cShared ? &pGMM->Shared : &pGMM->Private);
    }
    else
    {
        pChunk->cFree++;
        pChunk->pSet->cPages++;

        /*
         * If the chunk becomes empty, consider giving memory back to the host OS.
         *
         * The current strategy is to try give it back if there are other chunks
         * in this free list, meaning if there are at least 240 free pages in this
         * category. Note that since there are probably mappings of the chunk,
         * it won't be freed up instantly, which probably screws up this logic
         * a bit...
         */
        if (RT_UNLIKELY(   pChunk->cFree == GMM_CHUNK_NUM_PAGES
                        && pChunk->pFreeNext
                        && pChunk->pFreePrev))
            gmmR0FreeChunk(pGMM, pChunk);
    }
}


/**
 * Frees a shared page, the page is known to exist and be valid and such.
 *
 * @param   pGMM        Pointer to the GMM instance.
 * @param   idPage      The Page ID
 * @param   pPage       The page structure.
 */
DECLINLINE(void) gmmR0FreeSharedPage(PGMM pGMM, uint32_t idPage, PGMMPAGE pPage)
{
    PGMMCHUNK pChunk = gmmR0GetChunk(pGMM, idPage >> GMM_CHUNKID_SHIFT);
    Assert(pChunk);
    Assert(pChunk->cFree < GMM_CHUNK_NUM_PAGES);
    Assert(pChunk->cShared > 0);
    Assert(pGMM->cSharedPages > 0);
    Assert(pGMM->cAllocatedPages > 0);
    Assert(!pPage->Shared.cRefs);

    pChunk->cShared--;
    pGMM->cAllocatedPages--;
    pGMM->cSharedPages--;
    gmmR0FreePageWorker(pGMM, pChunk, pPage);
}


/**
 * Frees a private page, the page is known to exist and be valid and such.
 *
 * @param   pGMM        Pointer to the GMM instance.
 * @param   idPage      The Page ID
 * @param   pPage       The page structure.
 */
DECLINLINE(void) gmmR0FreePrivatePage(PGMM pGMM, uint32_t idPage, PGMMPAGE pPage)
{
    PGMMCHUNK pChunk = gmmR0GetChunk(pGMM, idPage >> GMM_CHUNKID_SHIFT);
    Assert(pChunk);
    Assert(pChunk->cFree < GMM_CHUNK_NUM_PAGES);
    Assert(pChunk->cPrivate > 0);
    Assert(pGMM->cAllocatedPages > 0);

    pChunk->cPrivate--;
    pGMM->cAllocatedPages--;
    gmmR0FreePageWorker(pGMM, pChunk, pPage);
}


/**
 * Common worker for GMMR0FreePages and GMMR0BalloonedPages.
 *
 * @returns VBox status code:
 * @retval  xxx
 *
 * @param   pGMM                Pointer to the GMM instance data.
 * @param   pGVM                Pointer to the shared VM structure.
 * @param   cPages              The number of pages to free.
 * @param   paPages             Pointer to the page descriptors.
 * @param   enmAccount          The account this relates to.
 */
static int gmmR0FreePages(PGMM pGMM, PGVM pGVM, uint32_t cPages, PGMMFREEPAGEDESC paPages, GMMACCOUNT enmAccount)
{
    /*
     * Check that the request isn't impossible wrt to the account status.
     */
    switch (enmAccount)
    {
        case GMMACCOUNT_BASE:
            if (RT_UNLIKELY(pGVM->gmm.s.Allocated.cBasePages < cPages))
            {
                Log(("gmmR0FreePages: allocated=%#llx cPages=%#x!\n", pGVM->gmm.s.Allocated.cBasePages, cPages));
                return VERR_GMM_ATTEMPT_TO_FREE_TOO_MUCH;
            }
            break;
        case GMMACCOUNT_SHADOW:
            if (RT_UNLIKELY(pGVM->gmm.s.Allocated.cShadowPages < cPages))
            {
                Log(("gmmR0FreePages: allocated=%#llx cPages=%#x!\n", pGVM->gmm.s.Allocated.cShadowPages, cPages));
                return VERR_GMM_ATTEMPT_TO_FREE_TOO_MUCH;
            }
            break;
        case GMMACCOUNT_FIXED:
            if (RT_UNLIKELY(pGVM->gmm.s.Allocated.cFixedPages < cPages))
            {
                Log(("gmmR0FreePages: allocated=%#llx cPages=%#x!\n", pGVM->gmm.s.Allocated.cFixedPages, cPages));
                return VERR_GMM_ATTEMPT_TO_FREE_TOO_MUCH;
            }
            break;
        default:
            AssertMsgFailedReturn(("enmAccount=%d\n", enmAccount), VERR_INTERNAL_ERROR);
    }

    /*
     * Walk the descriptors and free the pages.
     *
     * Statistics (except the account) are being updated as we go along,
     * unlike the alloc code. Also, stop on the first error.
     */
    int rc = VINF_SUCCESS;
    uint32_t iPage;
    for (iPage = 0; iPage < cPages; iPage++)
    {
        uint32_t idPage = paPages[iPage].idPage;
        PGMMPAGE pPage = gmmR0GetPage(pGMM, idPage);
        if (RT_LIKELY(pPage))
        {
            if (RT_LIKELY(GMM_PAGE_IS_PRIVATE(pPage)))
            {
                if (RT_LIKELY(pPage->Private.hGVM == pGVM->hSelf))
                {
                    Assert(pGVM->gmm.s.cPrivatePages);
                    pGVM->gmm.s.cPrivatePages--;
                    gmmR0FreePrivatePage(pGMM, idPage, pPage);
                }
                else
                {
                    Log(("gmmR0AllocatePages: #%#x/%#x: not owner! hGVM=%#x hSelf=%#x\n", iPage, idPage,
                         pPage->Private.hGVM, pGVM->hEMT));
                    rc = VERR_GMM_NOT_PAGE_OWNER;
                    break;
                }
            }
            else if (RT_LIKELY(GMM_PAGE_IS_SHARED(pPage)))
            {
                Assert(pGVM->gmm.s.cSharedPages);
                pGVM->gmm.s.cSharedPages--;
                Assert(pPage->Shared.cRefs);
                if (!--pPage->Shared.cRefs)
                    gmmR0FreeSharedPage(pGMM, idPage, pPage);
            }
            else
            {
                Log(("gmmR0AllocatePages: #%#x/%#x: already free!\n", iPage, idPage));
                rc = VERR_GMM_PAGE_ALREADY_FREE;
                break;
            }
        }
        else
        {
            Log(("gmmR0AllocatePages: #%#x/%#x: not found!\n", iPage, idPage));
            rc = VERR_GMM_PAGE_NOT_FOUND;
            break;
        }
        paPages[iPage].idPage = NIL_GMM_PAGEID;
    }

    /*
     * Update the account.
     */
    switch (enmAccount)
    {
        case GMMACCOUNT_BASE:   pGVM->gmm.s.Allocated.cBasePages   -= iPage;
        case GMMACCOUNT_SHADOW: pGVM->gmm.s.Allocated.cShadowPages -= iPage;
        case GMMACCOUNT_FIXED:  pGVM->gmm.s.Allocated.cFixedPages  -= iPage;
        default:
            AssertMsgFailedReturn(("enmAccount=%d\n", enmAccount), VERR_INTERNAL_ERROR);
    }

    /*
     * Any threshold stuff to be done here?
     */

    return rc;
}


/**
 * Free one or more pages.
 *
 * This is typically used at reset time or power off.
 *
 * @returns VBox status code:
 * @retval  xxx
 *
 * @param   pVM                 Pointer to the shared VM structure.
 * @param   cPages              The number of pages to allocate.
 * @param   paPages             Pointer to the page descriptors containing the Page IDs for each page.
 * @param   enmAccount          The account this relates to.
 * @thread  EMT.
 */
GMMR0DECL(int) GMMR0FreePages(PVM pVM, uint32_t cPages, PGMMFREEPAGEDESC paPages, GMMACCOUNT enmAccount)
{
    LogFlow(("GMMR0FreePages: pVM=%p cPages=%#x paPages=%p enmAccount=%d\n", pVM, cPages, paPages, enmAccount));

    /*
     * Validate input and get the basics.
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (!pGVM)
        return VERR_INVALID_PARAMETER;
    if (pGVM->hEMT != RTThreadNativeSelf())
        return VERR_NOT_OWNER;

    AssertPtrReturn(paPages, VERR_INVALID_PARAMETER);
    AssertMsgReturn(enmAccount > GMMACCOUNT_INVALID && enmAccount < GMMACCOUNT_END, ("%d\n", enmAccount), VERR_INVALID_PARAMETER);
    AssertMsgReturn(cPages > 0 && cPages < RT_BIT(32 - PAGE_SHIFT), ("%#x\n", cPages), VERR_INVALID_PARAMETER);

    for (unsigned iPage = 0; iPage < cPages; iPage++)
        AssertMsgReturn(    paPages[iPage].idPage <= GMM_PAGEID_LAST
                        /*||  paPages[iPage].idPage == NIL_GMM_PAGEID*/,
                        ("#%#x: %#x\n", iPage, paPages[iPage].idPage), VERR_INVALID_PARAMETER);

    /*
     * Take the semaphore and call the worker function.
     */
    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);

    rc = gmmR0FreePages(pGMM, pGVM, cPages, paPages, enmAccount);

    RTSemFastMutexRelease(pGMM->Mtx);
    LogFlow(("GMMR0FreePages: returns %Rrc\n", rc));
    return rc;
}


/**
 * VMMR0 request wrapper for GMMR0FreePages.
 *
 * @returns see GMMR0FreePages.
 * @param   pVM             Pointer to the shared VM structure.
 * @param   pReq            The request packet.
 */
GMMR0DECL(int) GMMR0FreePagesReq(PVM pVM, PGMMFREEPAGESREQ pReq)
{
    /*
     * Validate input and pass it on.
     */
    AssertPtrReturn(pVM, VERR_INVALID_POINTER);
    AssertPtrReturn(pReq, VERR_INVALID_POINTER);
    AssertMsgReturn(pReq->Hdr.cbReq >= RT_UOFFSETOF(GMMFREEPAGESREQ, aPages[0]),
                    ("%#x < %#x\n", pReq->Hdr.cbReq, RT_UOFFSETOF(GMMFREEPAGESREQ, aPages[0])),
                    VERR_INVALID_PARAMETER);
    AssertMsgReturn(pReq->Hdr.cbReq == RT_UOFFSETOF(GMMFREEPAGESREQ, aPages[pReq->cPages]),
                    ("%#x != %#x\n", pReq->Hdr.cbReq, RT_UOFFSETOF(GMMFREEPAGESREQ, aPages[pReq->cPages])),
                    VERR_INVALID_PARAMETER);

    return GMMR0FreePages(pVM, pReq->cPages, &pReq->aPages[0], pReq->enmAccount);
}


/**
 * Report back on a memory ballooning request.
 *
 * The request may or may not have been initiated by the GMM. If it was initiated
 * by the GMM it is important that this function is called even if no pages was
 * ballooned.
 *
 * Since the whole purpose of ballooning is to free up guest RAM pages, this API
 * may also be given a set of related pages to be freed. These pages are assumed
 * to be on the base account.
 *
 * @returns VBox status code:
 * @retval  xxx
 *
 * @param   pVM                 Pointer to the shared VM structure.
 * @param   cBalloonedPages     The number of pages that was ballooned.
 * @param   cPagesToFree        The number of pages to be freed.
 * @param   paPages             Pointer to the page descriptors for the pages that's to be freed.
 * @param   fCompleted          Indicates whether the ballooning request was completed (true) or
 *                              if there is more pages to come (false). If the ballooning was not
 *                              not triggered by the GMM, don't set this.
 * @thread  EMT.
 */
GMMR0DECL(int) GMMR0BalloonedPages(PVM pVM, uint32_t cBalloonedPages, uint32_t cPagesToFree, PGMMFREEPAGEDESC paPages, bool fCompleted)
{
    LogFlow(("GMMR0BalloonedPages: pVM=%p cBalloonedPages=%#x cPagestoFree=%#x paPages=%p enmAccount=%d fCompleted=%RTbool\n",
             pVM, cBalloonedPages, cPagesToFree, paPages, fCompleted));

    /*
     * Validate input and get the basics.
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (!pGVM)
        return VERR_INVALID_PARAMETER;
    if (pGVM->hEMT != RTThreadNativeSelf())
        return VERR_NOT_OWNER;

    AssertPtrReturn(paPages, VERR_INVALID_PARAMETER);
    AssertMsgReturn(cBalloonedPages >= 0 && cBalloonedPages < RT_BIT(32 - PAGE_SHIFT), ("%#x\n", cBalloonedPages), VERR_INVALID_PARAMETER);
    AssertMsgReturn(cPagesToFree >= 0 && cPagesToFree <= cBalloonedPages, ("%#x\n", cPagesToFree), VERR_INVALID_PARAMETER);

    for (unsigned iPage = 0; iPage < cPagesToFree; iPage++)
        AssertMsgReturn(    paPages[iPage].idPage <= GMM_PAGEID_LAST
                        /*||  paPages[iPage].idPage == NIL_GMM_PAGEID*/,
                        ("#%#x: %#x\n", iPage, paPages[iPage].idPage), VERR_INVALID_PARAMETER);

    /*
     * Take the sempahore and do some more validations.
     */
    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);
    if (pGVM->gmm.s.Allocated.cBasePages >= cPagesToFree)
    {
        /*
         * Record the ballooned memory.
         */
        pGMM->cBalloonedPages += cBalloonedPages;
        if (pGVM->gmm.s.cReqBalloonedPages)
        {
            pGVM->gmm.s.cBalloonedPages += cBalloonedPages;
            pGVM->gmm.s.cReqActuallyBalloonedPages += cBalloonedPages;
            if (fCompleted)
            {
                Log(("GMMR0BalloonedPages: +%#x - Global=%#llx;  / VM: Total=%#llx Req=%#llx Actual=%#llx (completed)\n", cBalloonedPages,
                     pGMM->cBalloonedPages, pGVM->gmm.s.cBalloonedPages, pGVM->gmm.s.cReqBalloonedPages, pGVM->gmm.s.cReqActuallyBalloonedPages));

                /*
                 * Anything we need to do here now when the request has been completed?
                 */
                pGVM->gmm.s.cReqBalloonedPages = 0;
            }
            else
                Log(("GMMR0BalloonedPages: +%#x - Global=%#llx / VM: Total=%#llx Req=%#llx Actual=%#llx (pending)\n", cBalloonedPages,
                     pGMM->cBalloonedPages, pGVM->gmm.s.cBalloonedPages, pGVM->gmm.s.cReqBalloonedPages, pGVM->gmm.s.cReqActuallyBalloonedPages));
        }
        else
        {
            pGVM->gmm.s.cBalloonedPages += cBalloonedPages;
            Log(("GMMR0BalloonedPages: +%#x - Global=%#llx / VM: Total=%#llx (user)\n",
                 cBalloonedPages, pGMM->cBalloonedPages, pGVM->gmm.s.cBalloonedPages));
        }

        /*
         * Any pages to free?
         */
        if (cPagesToFree)
            rc = gmmR0FreePages(pGMM, pGVM, cPagesToFree, paPages, GMMACCOUNT_BASE);
    }
    else
    {
        rc = VERR_GMM_ATTEMPT_TO_FREE_TOO_MUCH;
    }

    RTSemFastMutexRelease(pGMM->Mtx);
    LogFlow(("GMMR0BalloonedPages: returns %Rrc\n", rc));
    return rc;
}


/**
 * VMMR0 request wrapper for GMMR0BalloonedPages.
 *
 * @returns see GMMR0BalloonedPages.
 * @param   pVM             Pointer to the shared VM structure.
 * @param   pReq            The request packet.
 */
GMMR0DECL(int) GMMR0BalloonedPagesReq(PVM pVM, PGMMBALLOONEDPAGESREQ pReq)
{
    /*
     * Validate input and pass it on.
     */
    AssertPtrReturn(pVM, VERR_INVALID_POINTER);
    AssertPtrReturn(pReq, VERR_INVALID_POINTER);
    AssertMsgReturn(pReq->Hdr.cbReq >= RT_UOFFSETOF(GMMBALLOONEDPAGESREQ, aPages[0]),
                    ("%#x < %#x\n", pReq->Hdr.cbReq, RT_UOFFSETOF(GMMBALLOONEDPAGESREQ, aPages[0])),
                    VERR_INVALID_PARAMETER);
    AssertMsgReturn(pReq->Hdr.cbReq == RT_UOFFSETOF(GMMBALLOONEDPAGESREQ, aPages[pReq->cPagesToFree]),
                    ("%#x != %#x\n", pReq->Hdr.cbReq, RT_UOFFSETOF(GMMBALLOONEDPAGESREQ, aPages[pReq->cPagesToFree])),
                    VERR_INVALID_PARAMETER);

    return GMMR0BalloonedPages(pVM, pReq->cBalloonedPages, pReq->cPagesToFree, &pReq->aPages[0], pReq->fCompleted);
}


/**
 * Report balloon deflating.
 *
 * @returns VBox status code:
 * @retval  xxx
 *
 * @param   pVM                 Pointer to the shared VM structure.
 * @param   cPages              The number of pages that was let out of the balloon.
 * @thread  EMT.
 */
GMMR0DECL(int) GMMR0DeflatedBalloon(PVM pVM, uint32_t cPages)
{
    LogFlow(("GMMR0DeflatedBalloon: pVM=%p cPages=%#x\n", pVM, cPages));

    /*
     * Validate input and get the basics.
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (!pGVM)
        return VERR_INVALID_PARAMETER;
    if (pGVM->hEMT != RTThreadNativeSelf())
        return VERR_NOT_OWNER;

    AssertMsgReturn(cPages >= 0 && cPages < RT_BIT(32 - PAGE_SHIFT), ("%#x\n", cPages), VERR_INVALID_PARAMETER);

    /*
     * Take the sempahore and do some more validations.
     */
    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);

    if (pGVM->gmm.s.cBalloonedPages < cPages)
    {
        Assert(pGMM->cBalloonedPages >= pGVM->gmm.s.cBalloonedPages);

        /*
         * Record it.
         */
        pGMM->cBalloonedPages -= cPages;
        pGVM->gmm.s.cBalloonedPages -= cPages;
        if (pGVM->gmm.s.cReqDeflatePages)
        {
            Log(("GMMR0BalloonedPages: -%#x - Global=%#llx / VM: Total=%#llx Req=%#llx\n", cPages,
                 pGMM->cBalloonedPages, pGVM->gmm.s.cBalloonedPages, pGVM->gmm.s.cReqDeflatePages));

            /*
             * Anything we need to do here now when the request has been completed?
             */
            pGVM->gmm.s.cReqDeflatePages = 0;
        }
        else
            Log(("GMMR0BalloonedPages: -%#x - Global=%#llx / VM: Total=%#llx\n", cPages,
                 pGMM->cBalloonedPages, pGVM->gmm.s.cBalloonedPages));
    }
    else
    {
        Log(("GMMR0DeflatedBalloon: cBalloonedPages=%#llx cPages=%#x\n", pGVM->gmm.s.cBalloonedPages, cPages));
        rc = VERR_GMM_ATTEMPT_TO_DEFLATE_TOO_MUCH;
    }

    RTSemFastMutexRelease(pGMM->Mtx);
    LogFlow(("GMMR0BalloonedPages: returns %Rrc\n", rc));
    return rc;
}


/**
 * Unmaps a chunk previously mapped into the address space of the current process.
 *
 * @returns VBox status code.
 * @param   pGMM        Pointer to the GMM instance data.
 * @param   pGVM        Pointer to the Global VM structure.
 * @param   pChunk      Pointer to the chunk to be unmapped.
 */
static int gmmR0UnmapChunk(PGMM pGMM, PGVM pGVM, PGMMCHUNK pChunk)
{
    /*
     * Find the mapping and try unmapping it.
     */
    for (uint32_t i = 0; i < pChunk->cMappings; i++)
    {
        Assert(pChunk->paMappings[i].pGVM && pChunk->paMappings[i].MapObj != NIL_RTR0MEMOBJ);
        if (pChunk->paMappings[i].pGVM == pGVM)
        {
            /* unmap */
            int rc = RTR0MemObjFree(pChunk->paMappings[i].MapObj, false /* fFreeMappings (NA) */);
            if (RT_SUCCESS(rc))
            {
                /* update the record. */
                pChunk->cMappings--;
                if (i < pChunk->cMappings)
                    pChunk->paMappings[i] = pChunk->paMappings[pChunk->cMappings];
                pChunk->paMappings[pChunk->cMappings].MapObj = NIL_RTR0MEMOBJ;
                pChunk->paMappings[pChunk->cMappings].pGVM = NULL;
            }
            return rc;
        }
    }

    Log(("gmmR0MapChunk: Chunk %#x is not mapped into pGVM=%p/%#x\n", pChunk->Core.Key, pGVM, pGVM->hSelf));
    return VERR_GMM_CHUNK_NOT_MAPPED;
}


/**
 * Maps a chunk into the user address space of the current process.
 *
 * @returns VBox status code.
 * @param   pGMM        Pointer to the GMM instance data.
 * @param   pGVM        Pointer to the Global VM structure.
 * @param   pChunk      Pointer to the chunk to be mapped.
 * @param   ppvR3       Where to store the ring-3 address of the mapping.
 *                      In the VERR_GMM_CHUNK_ALREADY_MAPPED case, this will be
 *                      contain the address of the existing mapping.
 */
static int gmmR0MapChunk(PGMM pGMM, PGVM pGVM, PGMMCHUNK pChunk, PRTR3PTR ppvR3)
{
    /*
     * Check to see if the chunk is already mapped.
     */
    for (uint32_t i = 0; i < pChunk->cMappings; i++)
    {
        Assert(pChunk->paMappings[i].pGVM && pChunk->paMappings[i].MapObj != NIL_RTR0MEMOBJ);
        if (pChunk->paMappings[i].pGVM == pGVM)
        {
            *ppvR3 = RTR0MemObjAddressR3(pChunk->paMappings[i].MapObj);
            Log(("gmmR0MapChunk: chunk %#x is already mapped at %p!\n", pChunk->Core.Key, *ppvR3));
            return VERR_GMM_CHUNK_ALREADY_MAPPED;
        }
    }

    /*
     * Do the mapping.
     */
    RTR0MEMOBJ MapObj;
    int rc = RTR0MemObjMapUser(&MapObj, pChunk->MemObj, (RTR3PTR)-1, 0, RTMEM_PROT_READ | RTMEM_PROT_WRITE, NIL_RTR0PROCESS);
    if (RT_SUCCESS(rc))
    {
        /* reallocate the array? */
        if ((pChunk->cMappings & 1 /*7*/) == 0)
        {
            void *pvMappings = RTMemRealloc(pChunk->paMappings, (pChunk->cMappings + 2 /*8*/) * sizeof(pChunk->paMappings[0]));
            if (RT_UNLIKELY(pvMappings))
            {
                rc = RTR0MemObjFree(MapObj, false /* fFreeMappings (NA) */);
                AssertRC(rc);
                return VERR_NO_MEMORY;
            }
            pChunk->paMappings = (PGMMCHUNKMAP)pvMappings;
        }

        /* insert new entry */
        pChunk->paMappings[pChunk->cMappings].MapObj = MapObj;
        pChunk->paMappings[pChunk->cMappings].pGVM = pGVM;
        pChunk->cMappings++;

        *ppvR3 = RTR0MemObjAddressR3(MapObj);
    }

    return rc;
}


/**
 * Map a chunk and/or unmap another chunk.
 *
 * The mapping and unmapping applies to the current process.
 *
 * This API does two things because it saves a kernel call per mapping when
 * when the ring-3 mapping cache is full.
 *
 * @returns VBox status code.
 * @param   pVM             The VM.
 * @param   idChunkMap      The chunk to map. NIL_GMM_CHUNKID if nothing to map.
 * @param   idChunkUnmap    The chunk to unmap. NIL_GMM_CHUNKID if nothing to unmap.
 * @param   ppvR3           Where to store the address of the mapped chunk. NULL is ok if nothing to map.
 * @thread  EMT
 */
GMMR0DECL(int) GMMR0MapUnmapChunk(PVM pVM, uint32_t idChunkMap, uint32_t idChunkUnmap, PRTR3PTR ppvR3)
{
    LogFlow(("GMMR0MapUnmapChunk: pVM=%p idChunkMap=%#x idChunkUnmap=%#x ppvR3=%p\n",
             pVM, idChunkMap, idChunkUnmap, ppvR3));

    /*
     * Validate input and get the basics.
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (!pGVM)
        return VERR_INVALID_PARAMETER;
    if (pGVM->hEMT != RTThreadNativeSelf())
        return VERR_NOT_OWNER;

    AssertCompile(NIL_GMM_CHUNKID == 0);
    AssertMsgReturn(idChunkMap <= GMM_CHUNKID_LAST, ("%#x\n", idChunkMap), VERR_INVALID_PARAMETER);
    AssertMsgReturn(idChunkUnmap <= GMM_CHUNKID_LAST, ("%#x\n", idChunkUnmap), VERR_INVALID_PARAMETER);

    if (    idChunkMap == NIL_GMM_CHUNKID
        &&  idChunkUnmap == NIL_GMM_CHUNKID)
        return VERR_INVALID_PARAMETER;

    if (idChunkMap != NIL_GMM_CHUNKID)
    {
        AssertPtrReturn(ppvR3, VERR_INVALID_POINTER);
        *ppvR3 = NIL_RTR3PTR;
    }

    if (pGMM->fLegacyMode)
    {
        Log(("GMMR0MapUnmapChunk: legacy mode!\n"));
        return VERR_NOT_SUPPORTED;
    }

    /*
     * Take the semaphore and do the work.
     *
     * The unmapping is done last since it's easier to undo a mapping than
     * undoing an unmapping. The ring-3 mapping cache cannot not be so big
     * that it pushes the user virtual address space to within a chunk of
     * it it's limits, so, no problem here.
     */
    int rc = RTSemFastMutexRequest(pGMM->Mtx);
    AssertRC(rc);

    PGMMCHUNK pMap = NULL;
    if (idChunkMap != NIL_GVM_HANDLE)
    {
        pMap = gmmR0GetChunk(pGMM, idChunkMap);
        if (RT_LIKELY(pMap))
            rc = gmmR0MapChunk(pGMM, pGVM, pMap, ppvR3);
        else
        {
            Log(("GMMR0MapUnmapChunk: idChunkMap=%#x\n", idChunkMap));
            rc = VERR_GMM_CHUNK_NOT_FOUND;
        }
    }

    if (    idChunkUnmap != NIL_GMM_CHUNKID
        &&  RT_SUCCESS(rc))
    {
        PGMMCHUNK pUnmap = gmmR0GetChunk(pGMM, idChunkUnmap);
        if (RT_LIKELY(pUnmap))
            rc = gmmR0UnmapChunk(pGMM, pGVM, pUnmap);
        else
        {
            Log(("GMMR0MapUnmapChunk: idChunkUnmap=%#x\n", idChunkUnmap));
            rc = VERR_GMM_CHUNK_NOT_FOUND;
        }

        if (RT_FAILURE(rc) && pMap)
            gmmR0UnmapChunk(pGMM, pGVM, pMap);
    }

    RTSemFastMutexRelease(pGMM->Mtx);

    LogFlow(("GMMR0MapUnmapChunk: returns %Rrc\n", rc));
    return rc;
}


/**
 * VMMR0 request wrapper for GMMR0MapUnmapChunk.
 *
 * @returns see GMMR0MapUnmapChunk.
 * @param   pVM             Pointer to the shared VM structure.
 * @param   pReq            The request packet.
 */
GMMR0DECL(int)  GMMR0MapUnmapChunkReq(PVM pVM, PGMMMAPUNMAPCHUNKREQ pReq)
{
    /*
     * Validate input and pass it on.
     */
    AssertPtrReturn(pVM, VERR_INVALID_POINTER);
    AssertPtrReturn(pReq, VERR_INVALID_POINTER);
    AssertMsgReturn(pReq->Hdr.cbReq == sizeof(*pReq), ("%#x != %#x\n", pReq->Hdr.cbReq, sizeof(*pReq)), VERR_INVALID_PARAMETER);

    return GMMR0MapUnmapChunk(pVM, pReq->idChunkMap, pReq->idChunkUnmap, &pReq->pvR3);
}


/**
 * Legacy mode API for supplying pages.
 *
 * The specified user address points to a allocation chunk sized block that
 * will be locked down and used by the GMM when the GM asks for pages.
 *
 * @returns VBox status code.
 * @param   pVM             The VM.
 * @param   pvR3            Pointer to the chunk size memory block to lock down.
 */
GMMR0DECL(int) GMMR0SeedChunk(PVM pVM, RTR3PTR pvR3)
{
    /*
     * Validate input and get the basics.
     */
    PGMM pGMM;
    GMM_GET_VALID_INSTANCE(pGMM, VERR_INTERNAL_ERROR);
    PGVM pGVM = GVMMR0ByVM(pVM);
    if (!pGVM)
        return VERR_INVALID_PARAMETER;
    if (pGVM->hEMT != RTThreadNativeSelf())
        return VERR_NOT_OWNER;

    AssertPtrReturn(pvR3, VERR_INVALID_POINTER);
    AssertReturn(!(PAGE_OFFSET_MASK & pvR3), VERR_INVALID_POINTER);

    if (!pGMM->fLegacyMode)
    {
        Log(("GMMR0SeedChunk: not in legacy mode!\n"));
        return VERR_NOT_SUPPORTED;
    }

    /*
     * Lock the memory before taking the semaphore.
     */
    RTR0MEMOBJ MemObj;
    int rc = RTR0MemObjLockUser(&MemObj, pvR3, GMM_CHUNK_SIZE, NIL_RTR0PROCESS);
    if (RT_SUCCESS(rc))
    {
        /*
         * Take the semaphore and add a new chunk with our hGVM.
         */
        int rc = RTSemFastMutexRequest(pGMM->Mtx);
        AssertRC(rc);

        rc = gmmR0RegisterChunk(pGMM, &pGMM->Private, MemObj, pGVM->hSelf);

        RTSemFastMutexRelease(pGMM->Mtx);

        if (RT_FAILURE(rc))
            RTR0MemObjFree(MemObj, false /* fFreeMappings */);
    }

    return rc;
}